Patent Application
20130327994
The present invention relates to a method of manufacturing a circuit board for connecting wiring patterns formed on both surfaces through a via or a circuit board for connecting layers by a conductive paste, a reuse paste used therefor, and a method of manufacturing the reuse paste.
In recent years, with a reduction in a size and an increase in a density of electronic components, a double-sided board or a multilayer board rather than a conventional single-sided board has been frequently used as a circuit board to be provided with electronic components. Furthermore, as a structure of the circuit board, an inner via hole structure is proposed in place of conventionally widely used through-hole processing and plating. The inner via hole structure is provided by a method of connecting layers by using a conductive paste, which enables high density wiring to be carried out. A method of manufacturing a circuit board using such a conductive paste is described with reference to
For prior art literatures regarding the present invention, the following Patent Literatures 1 and 2 are known.
A method of manufacturing a reuse paste includes preparing a fiber piece housing paste, producing a filtered recovery paste, and producing a reuse paste. In the preparing of the fiber piece housing paste, a conductive paste including a conductive powder, resin and a latent curing agent, and a fiber piece housing paste including a fiber piece dropping off from a prepreg used for manufacturing a circuit board are prepared. In the producing of the filtered recovery paste, the filtered recovery paste is produced by filtering the fiber piece housing paste, which remains in a paste state, by using a filter. In the production of the reuse paste, the reuse paste is produced by adding at least one of a solvent, resin, and a paste having a different composition from that of the filtered recovery paste into the filtered recovery paste.
Conductive paste 105 includes a conductive powder (conductive particle), resin as a main agent, and a latent curing agent. As the conductive powder, for example, copper powder having an average particle diameter of not less than 0.5 μm and not more than 20 μm and a specific surface area of not less than 0.1 m2/g and not more than 1.5 m2/g is used. As the main agent, for example, liquid epoxy resin is used. As the curing agent, for example, a latent curing agent is used. Use of the latent curing agent enables stable storage at an ordinary temperature to be carried out and variation during manufacture to be suppressed. It is preferable that a particle diameter of the latent curing agent is not less than 0.5 μm and not more than 30 μm. When the particle diameter is more than 30 μm, an unreacted latent curing agent may remain. When the particle diameter of the latent curing agent is less than 0.5 μm, curing may proceed at once, and the latent curing agent may be removed at the time when the paste is filtered by using the below-mentioned filter. Furthermore, it is preferable that a solid latent curing agent is used because, in the case of a liquid latent curing agent, the ratio of the latent curing agent and the resin as the main agent may largely vary when printing is repeated. As the latent curing agent, an amine-based latent curing agent, an amine adduct-based latent curing agent, a hydrazide-based latent curing agent, an imidazole-based latent curing agent, a dicyandiamide (DICY)-based latent curing agent, or a complex thereof are used.
Conductive paste 105 includes not less than 80 wt. % and not more than 92 wt. % of conductive powder, not less than 4.5 wt. % and not more than 17 wt. % of main agent, and not less than 0.5 wt. % and not more than 5 wt. % of latent curing agent.
Conductive powder 105 may be silver powder, alloy powder, solder powder, Ag-coated powder, or a mixture thereof, having an average particle diameter of not less than 0.5 μm and not more than 20 μm.
Fiber piece 108 is a foreign substance, which drops off from a cut surface of first prepreg 101, has semi-cured epoxy resin attached thereto, and is formed of a glass fiber or a fiber such as aramid, and may be a fiber piece group to which a plurality of fiber pieces are bound with resin.
In
It is desirable that jig 104 should be pushed by a predetermined pressure or more so as to be brought into close contact with the surface of first protective film 102. By setting the pressure of jig 104 to be the predetermined pressure or more, an amount of conductive paste 105 (not shown) that is left as a residue on the surface of first protective film 102 can be reduced. As a result, it is possible to reduce conductive paste 105 to be discarded in a state in which it is attached to first protective film 102.
In order to reduce the amount of conductive paste 105 to be discarded in a state in which it is attached to the surface of first protective film 102, it is desirable that conductive particles included in conductive paste 105 should be properly scraped out such that they are not left on the surface of first protective film 102. Herein, as the conductive particle, for example, a copper particle having a particle diameter of about 1 μm to 10 μm is used. As the scraping is carried out more certainly on first protective film 102 by using jig 104, fiber pieces 108 attached to first protective film 102 are housed in conductive paste 105. Hereinafter, the diameter of fiber piece 108 may be not less than 1 μm and furthermore, not less than 5 μm, or may be equal to or larger than the particle diameter of copper particle.
As shown in
When a member having a selective permeability with respect to components of conductive paste 105 is used as the breathable sheet, only a part of the components of conductive paste 105 may be selectively absorbed through the breathable sheet. Therefore, the composition of fiber piece housing paste 109 may be influenced. Herein, examples of the components of conductive paste 105 include a liquid component or a solvent component. The composition of fiber piece housing paste 109 includes, for example, a ratio of a solid content or a liquid component.
In
By laminating an insulating layer, a wiring or the like on the both surfaces with first circuit board 115 as a core substrate, a multilayer structure can be formed.
In
As mentioned above, when conductive paste 105 is filled in first hole 103 formed in first prepreg 101 through first protective film 102, fiber piece 108 attached to first prepreg 101 is mixed into conductive paste 105, which may influence electrical characteristics. This becomes more remarkable as a diameter of the via becomes smaller.
Such a problem caused by fiber piece 108 hardly arises in a screen printing method which is widely used in manufacture of a circuit board or the like. This is because a screen print (particularly, an emulsion used therein) prevents contact between fiber piece 108 and conductive paste 105 in the screen printing method. Also in a conventional method of manufacturing a circuit board by connecting layers through plating, the problem hardly arises.
As shown in
Recently, increase in a density of a circuit board and reduction in a diameter of the via have been demanded. The smaller the diameter of the via becomes, the more easily a resistance of the via or the like is influenced by the mixture of the fiber pieces. For this reason, the conductive paste having the fiber piece mixed therein has been discarded.
First prepreg 101 contains a fiber such as glass or aramid and semi-cured resin. Since semi-cured epoxy resin is in an uncured state, it is fragile, small and broken easily. Furthermore, in order to impregnate the fiber with the epoxy resin without generating an air bubble, a fiber-opening processing for disentangling fibers is carried out. Consequently, fiber pieces 108 or semi-cured resin attached to the fiber tends to drop off from a side surface or a cut surface of first prepreg 101.
Furthermore, the dropping resin or fiber piece 108 is easily attached to a surface of other stacked first prepregs 101 with static electricity or the like. This is because first prepreg 101, fiber piece 108, and semi-cured resin are insulating materials and are easily charged with static electricity. Furthermore, several tens of first prepregs 101 (for example, a sheet shape of 500 mm×600 mm) are stacked in a thickness direction before manufacture, and are peeled off one by one and processed singly during manufacture in many cases. Therefore, first prepreg 101 is easily charged with the static electricity during the stacking or peeling, and fiber pieces 108 or the like dropping off from the side surface of first prepreg 101 are attached to first prepreg 101. Even if fiber piece 108 is removed by, for example, an adhesive roll in a process, new fiber piece 108 may be attached when first prepreg 101 is charged at a next process. Furthermore, even in first prepreg 101 from which static electricity is removed, new static electricity is generated when each of first prepregs 101 is peeled one by one after the lamination.
A state in which a waste paste is recycled is described with reference to
Recovery pastes 119a to 119d are pastes used in separate squeezing processes or separate processes for filling a conductive paste, or used paste attached to separate jig 104, and are conventionally treated as an industrial waste.
Recovery pastes 119a to 119d includes composition deviation pastes 116a to 116d in which composition deviation occurs due to squeezing, or the like and fiber pieces 108a to 108d.
A large number of recovery pastes 119a to 119d are generated in small amounts at the respective processes. Furthermore, in composition deviation pastes 116a to 116d included in recovery pastes 119a to 119d, a composition rate of conductive powder, resin or the like included therein deviates from a standard value in a manufacturing specification. Conductive paste 105 includes conductive powder, a main agent and a latent curing agent. As the number of printing times is increased, the number of fiber pieces 108 in conductive paste 105 is increased, and the amount of the conductive powder is increased. As a result, the composition deviates.
Furthermore, since conductive powders or latent curing agents rub each other by squeezing, an aggregate may be generated. When a latent curing agent as a large aggregate enters the via, it apparently acts as a latent curing agent having a large particle diameter. That is to say, at the time of pressing, an unreacted latent curing agent is left, and this unreacted latent curing agent prevents the contact between the conductive powder in the via. As a result, the resistance value of conductive paste 105 is increased, and the via resistance is increased.
The composition rate is changed according to conditions for squeezing (or conditions for being rubbed), frequency of using paste, or influence of first protective film 102, first hole 103, or the like. Furthermore, types and amounts of fiber pieces 108a to 108d or an aggregate included in recovery pastes 119a to 119d are varied depending on a difference in a type of a base material, an environment, a processing device or a handling device, the number of filling printing, a viscosity of paste, or the like.
A large amount of a plurality of different lots or fiber piece housing paste 109 housing a plurality of fiber pieces obtained in the squeezing process are recovered as a plurality of recovery pastes 119a to 119d. Then, they are gathered into one so as to form recovered composite paste 120.
By recovering a plurality of types of used pastes and unifying them into one so as to form recovered composite paste 120, it is possible to increase an amount of reproduction per time. As a result, a cost of reproduction can be reduced. Note here that recovered composite paste 120 includes various fiber pieces 108a to 108d.
Even if recovery pastes 119a to 119d have different compositions or the like from each other, when they are recovered as a single batch, it is possible to reduce a waste generated in a reproducing process.
Even if recovery pastes 119a to 119d can be recovered in a small amount, for example, about 10 g to 50 g per lot, when a plurality of such small-amount lots are gathered periodically if necessary, recovered composite paste 120 can be made to be not less than 1 kg to 10 kg. As a result, the yield during recycling can be increased, and the process cost can be suppressed. Herein, the plurality of lots mean, for example, 10 to 100 lots or more.
It is desirable that an opening diameter of filter 121 should be adjusted in the filtration process of recovered composite paste 120. Specifically, it is desirable that the opening diameter of filter 121 should be not less than three times as large as an average diameter of metal particles included in recovered composite paste 120, and not more than 20 times, further desirably not more than 10 times, and yet further desirably not more than 5 times as large as an average diameter of fibers constituting first prepreg 101. This is because when fibers such as glass fiber are included as a foreign substance in recovered composite paste 120, a length of the glass fiber as the foreign substance is not less than 20 times and further not less than 50 times as great as the average diameter of the glass fiber.
Furthermore, the aggregated conductive powder or the aggregate of the latent curing agent is disentangled by filtration using filter 121. That is to say, since foreign substances are removed and the aggregate is disentangled through a filtration process, filtered recovery paste 122 having a stable resistance value can be obtained.
It is preferable that the opening diameter of filter 121 is not less than three times as large as an average particle diameter of the conductive particles, not more than 20 times as large as an average diameter of fiber pieces 108, and not more than twice as large as the diameter of the latent curing agent.
The latent curing agent is produced by, for example, allowing several types of amines and epoxy resin to react with each other to make them into particles. The latent curing agent can be stored at room temperature for a long time in a state in which the property thereof is not changed, and it is cured when it is heated to a predetermined temperature or higher. When the latent curing agent is used, even if reproduction of conductive paste 105 is carried out many times, more stable printing can be carried out.
It is preferable that the latent curing agent has a softening temperature of not less than 80° C. and not more than 180° C. When the softening temperature is less than 80° C., a storage property at ordinary temperature is deteriorated. Furthermore, since a viscosity is increased when it is left at ordinary temperature, conductive paste 105 may not easily enter into the via, and may not be easily filtered. When the softening temperature is more than 180° C., the latent curing agent is not sufficiently melted during pressing, curing of resin as a main agent becomes insufficient, or the latent curing agent that has not been able to be melted remain, and space with which the conductive powder is not brought into contact remains, thus increasing the via resistance in some cases.
By adding a small amount of an organic solvent or the like to recovered composite paste 120 if necessary, a viscosity of recovered composite paste 120 can be lowered. As a result, workability of filtration of filter 121 can be enhanced. Furthermore, it is preferable that the organic solvent or the like, which has been added for filtration, may be appropriately taken out from a solvent or the like to be added later to filtered recovery paste 122 if necessary. In this way, recovered composite paste 120 is filtered in a state in which it remains in a paste state.
Solvent 123 or the like is at least any one of a solvent, resin and a paste having a different composition from that of filtered paste. As the solvent, a solvent that is the same solvent as that included in the conductive paste is used. Alternatively, as the solvent, for example, Diethylene glycol monobutyl ether acetate another name of which is Butyl Carbitol Acetate is used. As the resin, resin that is the same as that included in the conductive paste is used. Alternatively, as the resin, epoxy resin or the like is used. Solvent 123 or the like may be added and mixed at one time or separately at a plurality of times. Furthermore, after the viscosity is reduced, filtration is carried out, so that filtered recovery paste 122 may be obtained. Reuse paste 124 is a conductive paste which is reproduced for reuse by removing fiber piece 108 from the used conductive paste without influencing a shape or the like of, for example, copper powder included therein. It is useful to adjust reuse paste 124 to have a composition, a solid content, a viscosity or the like which is substantially the same as that of brand-new conductive paste 105 described in
Note here that solvent 123 or the like may be not only an organic solvent but also liquid thermosetting resin or other conductive pastes. When a conductive paste is used as solvent 123 or the like, it is useful to use another conductive paste having a different viscosity and composition ratio from those of conductive paste 105 described in, for example,
It is useful that a kneading device (for example, a planetary mixer or a roll kneading device) is used for mixing filtered recovery paste 122 and solvent 123 or the like.
Herein, it is desirable to use a viscometer for adjusting a viscosity (or measuring the viscosity). Furthermore, it is desirable to use a solid content meter for adjusting a composition ratio (or measuring the composition ratio) or to use a thermal analyzer (which is referred to as DSC, TG, DTA or the like). When conductive powder included in recovery pastes 119a to 119d is base metal (for example, copper), it is useful that the composition ratio is measured and adjusted by thermogravimetry (TG) in a nitrogen atmosphere in order to prevent the influence of oxidation of conductive powder.
Note here that the composition ratio denotes an amount (wt. %) of conductive powder in a paste, an amount (wt. %) of a volatile matter in a paste, an amount (wt. %) of an organic matter in a paste, or the like. Furthermore, since the specific gravity of the paste is largely influenced by a content rate of metal contained in the paste, a specific gravity of the paste may be refereed to. When the specific gravity is measured, a floating method, a specific gravity bottle method, method (a pycnometer method), a vibration type density meter, a balance method, or the like, may be used based on JIS K 0061 (Test methods for density and relative density of chemical products). When the pycnometer method is used, a commercially available specific gravity bottle may be used. Herein, a Wadon type, Gay-Lussac type, LeCharite type or JIS K 2249 Harvard type specific gravity bottle is used for measuring specific gravities of liquid and semisolid paving tars having a relatively high viscosity. In the case of a paste having a high viscosity, it is also useful to self-make a specific gravity bottom itself. When a specific gravity bottle having a volume of about 1 cc to 100 cc is self-made, it is useful to use metal materials such as stainless steel. By self-making a specific gravity bottle made of stainless steel, it is possible to prevent damage during measurement or in handling or the like, and facilitating smear washing with a solvent or the like can be carried out easily.
It is useful that fibers each having a length of not less than 10 times as great as an average particle diameter of conductive powders included in fiber piece housing paste 109 occupy not less than 50 wt % in all fiber pieces 108. This is because fibers each having the length of not less than 10 times as great as the average particle diameter of the conductive powders are easily removed in the filtration process. When fibers each having the length of not less than 10 times as great as the average particle diameter of the conductive powders occupy less than 50 wt. % in all fiber pieces 108 included in fiber piece housing paste 109, that is to say, fiber pieces having the length of less than 10 times as great as an average particle diameter of the conductive powders are included in a large amount, the rate of fiber pieces included in reuse paste 124 is increased. That is to say, fiber pieces that have not been able to be removed by filtration are increased. As a result, a property as reuse paste 124 may be influenced.
Furthermore, it is useful that fiber piece housing paste 109 includes not less than 50 wt % and less than 90 wt % of fibers each having the length of not less than 10 times and less than 100 times as great as an average particle diameter of the conductive powders with respect to all fiber pieces 108. When fibers each having a length of not less than 100 times as great as the average particle diameter of the conductive powders are present, or fibers each having a length of not less than 10 times as large as the average particle diameter are present in 90 wt % or more, filtration may be difficult.
Furthermore, by setting fibers included in fiber piece housing paste 109 and having a length of not less than 10 times as great as the average particle diameter of the conductive powders to be not less than 0.01 wt % and not more than 10 wt % with respect to fiber piece housing paste 109, reuse paste 124 can be easily manufactured. When the amount of fibers included in fiber piece housing paste 109 and having the length of not less than 10 times as great as the average particle diameter of the conductive powders is less than 0.01 wt % with respect to fiber piece housing paste 109, a removing effect of long fibers in the filtration process may not be obtained. Furthermore, when it is not less than 10.00 wt %, filtration may be difficult.
It is desirable that fiber piece 108 included in fiber piece housing paste 109 should be a glass fiber or an aramid fiber. Note here that the glass fiber is a part of a glass woven fabric or a glass nonwoven fabric constituting the core material of the prepreg. Furthermore, the aramid fiber is also a part of woven fabric or an aramid nonwoven fabric constituting the core material of the prepreg.
Furthermore, it is desirable that an opening diameter of the filter to be used in filtration should be not less than three times as large as an average particle diameter of the conductive powders included in fiber piece housing paste 109, and not more than 20 times as large as the average diameter of fiber pieces 108. When the opening diameter is less than three times as large as the average particle diameter, a filtration effect of the conductive powder may be influenced. Furthermore, when it is more than 20 times as large as the average diameter, a removing property of long fibers may be influenced.
In the filtration process, it is useful to keep a temperature of fiber piece housing paste 109 at a temperature range of not less than 0° C. and less than 80° C. When the temperature is less than 0° C., caution is required in handling. When the temperature is not less than 80° C., thermosetting resin included in reuse paste 124 may start to be cured.
In reuse paste 124, it is useful that the rate of fibers each having a length of not less than 10 times as great as an average particle diameter of the conductive powders is made to be not less than 10 wt. % in all fiber pieces. When the rate of long fibers is made to be not more than 10 wt % and furthermore not more than 5 wt %, the increase in a viscosity during the manufacturing process for manufacturing a circuit board by using reuse paste 124 can be reduced.
Furthermore, it is useful to suppress the rate of the fiber pieces having a length of less than three times as large as an average particle diameter of conductive powders included in reuse paste 124 to not more than 5 wt % with respect to the weight of all reuse pastes 124. When the rate is made to be not more than 5 wt %, it is possible to reduce the increase in a viscosity during the manufacturing process when a circuit board is manufactured by using reuse paste 124.
Next, a state in which a second circuit board is manufactured by using reuse paste 124 thus produced is described with reference to
Second protective film 126 is applied to both surfaces of second prepreg 125. Fiber pieces 108 such as a glass fiber may be attached to the surface of second protective film 126. Fiber pieces 108 may not be able to be removed by a suction device or an adhesive roll (both are not shown in the drawing).
As shown in
When pressurizing (further desirably, heating) is carried out in the direction of arrow 707, a state shown in
Second copper foil 128 shown in
Next, with reference to
A particle diameter or a shape of conductive powder 134, a particle size distribution or the like can be optimized depending on respective applications of uses. As shown in
In this exemplary embodiment, waste pastes, which are conventionally discarded, are recovered as recovery pastes 119a to 119d and then gathered into recovered composite paste 120. Then, fiber piece 108 is selectively removed from recovered composite paste 120, and a viscosity or a solid part, a composition ratio, or the like, is adjusted. Then, it is reproduced as a reuse paste. Thus, a circuit board is manufactured.
In this exemplary embodiment, fiber piece housing paste 109, which is generated in processes of
In
As shown in
Furthermore, when the viscosity of the conductive paste before printing is 15 (Pa·s), the viscosity after 250 sheets are printed is about 89 (Pa·s) (see the below-mentioned Table 1). Only when a new conductive paste is added without adjusting the viscosity of the conductive paste, after 250 sheets are printed, the viscosity becomes higher than 50 (Pa·s). When the viscosity is high, a filling property into first hole 103 may be influenced. When the initial viscosity of the reuse paste is more than 50 Pa·s, the number of sheets to be able to be printed thereafter may be reduced. Therefore, it is preferable that the viscosity before the start of printing is adjusted to be not less than 5 (Pa·s) and not more than 50 (Pa·s). That is to say, in this exemplary embodiment, it is important to adjust the viscosity of the used conductive paste and to filter the used conductive paste by using a filter.
Hereinafter, reuse according to this exemplary embodiment is described. The present invention proposes not simple reuse of a used conductive paste but any of highly advanced technical ideas utilizing a natural law for reuse. It is thought that decrease in an amount of discard of conductive pastes, and furthermore, the reuse of the conductive pastes in the present invention correspond to reuse, which is reuse with the same purpose as that in the beginning, including continuous use in EU (for example, in WEEE (Waste Electrical and Electronic Equipment) Directive, Article 7).
In particular, in EU (for example, WEEE Directive, Article 7), recycle is divided into two categories, that is, recovery and disposal. Furthermore, the recovery is divided into three categories, that is, reuse, recycle and energy recovery. Herein, the disposal denotes redemption or landfill. The reuse denotes that use is carried out again for the same purpose as that in the beginning including the continuous use. The recycle denotes reprocessing of a waste material for the purpose in the beginning or the other purpose in the production process. The energy recovery denotes energy recovery through direct combustion accompanied by thermal recovery.
This exemplary embodiment corresponds to the recovery in the definition of the recycle in EU and is useful for reduction in waste or the like or reduction in consumption of resource energy or the like.
Even if a conductive paste is simply mixed into a used conductive paste (or conductive paste being used) on a metal mask having a smaller opening portion than that of a material to be printed, fiber pieces or the like to be mixed (further stored) in the conductive paste cannot be removed. Therefore, the used conductive paste (or the conductive paste to be used for reuse) according to this exemplary embodiment is recovered to an outside of a printing machine through the metal mask or the like provided in the periphery of the material to be printed.
In this exemplary embodiment, the used conductive paste is taken out (or recovered) from the metal mask or the like (and furthermore, a used printing machine, squeegee or the like) provided in the vicinity of the material to be printed, and the conductive paste is recycled (particularly, reused) in the outside of the printing machine (or in another place, another device). When the used conductive paste is taken out in this way, the used conductive pastes generated in a plurality of different print lots on different days and times are efficiently recovered and are thus gathered into a single large lot (not less than 1 kg, not less than 5 kg, and furthermore, not less than 10 kg). Therefore, efficiency or yield of recycle (particularly, reuse) of the conductive paste can be enhanced. An amount of the used conductive paste generated after printing is completed is small (for example, less than 1 kg, and further 500 g to 50 g). When printing is carried out by using a squeegee, when the amount of the conductive paste is decreased, the conductive paste is scattered discontinuously on the linear contact surface of the squeegee and the material to be printed, and cannot be filled in the holes formed in the prepreg. By gathering a plurality of the conductive pastes in small amounts to increase the amount (not less than 1 kg and further not less than 10 kg) rather than recovering them in a small amounts, the fiber pieces or the like in the used paste can be removed with a high efficiency.
In this exemplary embodiment, recovered conductive pastes are reproduced such that they can be reused with a dispersion state of conductive particles maintained as it is. Thus, this exemplary embodiment proposes a highly advanced technical idea.
Hereinafter, this exemplary embodiment is described in more detail. Tables 1 to 5 show an example of the result obtained by an experiment for the effects in this exemplary embodiment.
Tables 1 to 5 show diameters and the number of the holes formed in the prepreg, and defect rates when the number of printed sheets is varied. Furthermore, a right end of each Table shows a viscosity for each number of printed sheets. By using a cone-plate type rheometer, an apparent viscosity at 0.5 rpm is measured. A unit of the viscosity is Pa·s. The cone of the cone-plate type rheometer has a diameter of 25 mm and a cone angle of 2°. A measurement temperature of the sample is 25° C. Measurement of viscosity or the like is based on JIS K7117-2.
Prepreg (500 mm×600 mm) is provided with 50000 holes in total including 10000 holes each having a diameter of 80 μm, 10000 holes each having a diameter of 100 μm, 10000 holes each having a diameter of 130 μm, 10000 holes each having a diameter of 150 μm, and 10000 holes each having a diameter of 200 μm. Table 1 shows the results obtained by evaluating them using a test pattern capable of carrying out evaluation in a single prepreg. As the conductive paste, paste obtained by kneading spherical copper powder having a center particle diameter of 7 μm, epoxy resin and a latent curing agent having a particle diameter of 15 μm by using three-roller is used. In the Table 1, the number of vias which have conduction defect is measured in 10000 holes. Note here that generally widely used via chain pattern, that is, a test pattern for measuring whether or not one disconnected via is present in 10000 continuous vias is not used. Furthermore, when 10000 holes each having a diameter of 130 μm are formed, a yield obtained when 350 sheets are printed is set to be 1.0 as normalization. For this reason, a unit is not given to the defect rate in the Table 1. In Table 1, φ represents a diameter of a hole.
From the result of the 50th printed sheet in Table 1, a defect does not occur in the case of the holes having the diameters of 80 μm to 200 μm. The viscosity at this time is 20 (Pa·s).
From the result of the 250th printed sheet in Table 1, a defect does not occur in the case of the holes having the diameters of 80 μm to 200 μm. The viscosity at this time is 89 (Pa·s). It is shown that the viscosity is increased as the number of printed sheets is increased.
From the result of the 300th printed sheet in Table 1, the defect rate is 7.5 in the case of the holes having a diameter of 80 μm, and the defect rate is 1.7 in the case of the holes having a diameter of 100 μm. The defect does not occur in the case of the holes having diameters of 130 to 200 μm. As mentioned above, it is shown that when the number of the printed sheets is increased to 300, the defect rate is increased as the diameter of the hole is decreased. Furthermore, the viscosity at the time when the number of printed sheets is 300 is 137 (Pa·s), and the defect does not occur for the 300th sheet in the case of the holes having the diameters of 130 to 200 μm. The defect occurs when the diameter of the hole is not more than 100 μm, and the defect does not occur when the diameter of the hole is not less than 130 μm. This is thought to be as follows. Since the holes each having a diameter of 130 to 200 μm have larger diameters as compared with the holes having diameters of 80 to 100 μm, even when the viscosity of the conductive paste is increased to 137 (Pa·s), the conductive paste can be filled in the hole reliably.
From the result when the number of printed sheets is 350 in Table 1, the defect rate is 14.5 for 10000 holes each having a diameter of 80 μm, 5.8 for 10000 holes each having a diameter of 100 μm, and 1.0 for 10000 holes each having a diameter of 130 μm (because this value is normalized as 1.0). Note here that the defect rate is 0 for holes having diameters of 150 μm and 200 μm. This is thought to be as follows. Although the viscosity of the paste is further increased to 169 (Pa·s), the diameter of the hole is large, that is, not less than 150 μm, so that conductive pastes can be filled in the holes reliably.
From the result when the number of printed sheets is 400 in Table 1, the defect rate is 33.2 for 10000 holes each having a diameter of 80 μm, 9.9 for 10000 holes each having a diameter of 100 μm, 3.8 for 10000 holes each having a diameter of 130 μm, and 1.2 for 10000 holes each having a diameter of 150 μm. Note here that the defect rate is 0 for holes each having a diameter of 200 μm. This is thought to be as follows. Although the viscosity of the paste is further increased to 247 (Pa·s), the diameter of the hole is large, that is, 200 μm, so that conductive pastes can be filled in the holes reliably.
From the result when the number of printed sheets is 450 in Table 1, the defect rate is 63.9 for 10000 holes each having a diameter of 80 μm, 21.4 for 10000 holes each having a diameter of 100 μm, 10.3 for 10000 holes each having a diameter of 130, 3.8 for 10000 holes each having a diameter of 150 μm, and 0.9 for 10000 holes each having a diameter of 200 μm. Note here that a defect occurs even when the diameter of the hole is 200 μm. This is thought to be because when as many as 450 sheets are printed, a viscosity of ink is largely increased to 511 (Pa·s), so that the conductive paste cannot be filled in the holes although a diameter of each hole is large, that is, 200 μm.
When the diameter of the hole is smaller than 130 μm, a defect does not occur when the viscosity of the conductive paste is 89 (Pa·s), but a defect occurs when the viscosity of the conductive paste is 137 (Pa·s). Therefore, it is desirable that when the viscosity of the conductive paste is not less than about 80 (Pa·s), the conductive pastes which have not been filled in the holes should be recovered as the recovery paste. Since the initial viscosity (the viscosity before the start of printing) of the conductive paste is 15 (Pa·s), when the viscosity becomes not less than about 5 times as large as the initial viscosity, the conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
When the diameter of the hole is not less than 130 μm and less than 150 μm, a defect does not occur when the viscosity of the conductive paste is 137 (Pa·s), but a defect occurs when the viscosity of the conductive paste is 169 (Pa·s). Therefore, it is desirable that when the viscosity of the conductive paste is not less than about 130 (Pa·s), the conductive pastes which have not been filled in the holes should be recovered as the recovery paste. Since the initial viscosity of the conductive paste is 15 (Pa·s), when the viscosity becomes not less than about 8 times as large as the initial viscosity, the conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
When the diameter of the hole is not less than 150 μm and less than 200 μm, a defect does not occur when the viscosity of the conductive paste is 169 (Pa·s), but a defect occurs when the viscosity of the conductive paste is 247 (Pa·s). Therefore, it is desirable that when the viscosity of the conductive paste is not less than about 160 (Pa·s), the conductive pastes which have not been filled in the holes should be recovered as the recovery paste. Since the initial viscosity of the conductive paste is 15 (Pa·s), when the viscosity becomes not less than about 10 times as large as the initial viscosity, the conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
When the diameter of the hole is not less than 200 μm, a defect does not occur when the viscosity of the conductive paste is 247 (Pa·s), but a defect occurs when the viscosity of the conductive paste is 511 (Pa·s). Therefore, it is desirable that when the viscosity of the conductive paste is not less than about 240 (Pa·s), the conductive pastes which have not been filled in the holes should be recovered as the recovery paste. Since the initial viscosity of the conductive paste is 15 (Pa·s), when the viscosity becomes not less than about 16 times as large as the initial viscosity, the conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
It may be difficult to precisely obtain measurement values of the viscosity in processes every measurement time. In such a case, it is useful to measure what times the viscosity after printing is as large as the initial viscosity where the initial viscosity (before start of printing) is defined as 1, and to recover the conductive pastes which have not been filled in the hole as a recovery paste. Herein, the viscosity before the start of printing is defined as 1, but the viscosity after predetermined number of sheets (for example, ten sheets) are printed may be defined as 1.
Furthermore, as shown in Table 1, relation between the viscosity and the number of printed sheets at which a defect occurs is previously examined, and the conductive pastes which have not been filled in the hole after a predetermined number of sheets are printed may be recovered as the recovery paste.
Note here that the diameter of the hole of 80 μm means in detail the diameter of 80 μm±8 μm. The diameter of the hole of 100 μm means in detail the diameter of 100 μm±10 μm. The diameter of the hole of 130 μm means in detail the diameter of 130 μm±13 μm. The diameter of the hole of 150 μm means in detail the diameter of 150 μm±15 μm. The diameter of the hole of 200 μm means in detail the diameter of 200 μm±20 μm. This is because variation occurs in the diameters of the holes. Note here that it is useful that the diameter of the hole is a diameter in the portion whose sectional area is a minimum.
Conventionally, when the number of printed sheets is a predetermined number or more, conductive pastes are discarded regardless of a diameter of a hole. A used conductive paste may cause defects in a small hole whose diameter is 80 μm, but defects may not occur in a relatively large hole whose diameter is 200 μm. Conventionally, however, a conductive paste that can be used by selecting a diameter of a hole may be discarded in many cases.
In this exemplary embodiment, conductive pastes exceeding the number of the printed sheets, that is, 450 in the Table 1 which are conventionally discarded are recovered as recovery pastes 119a to 119d. Furthermore, the used conductive pastes are united with used conductive pastes in other lots so as to prepare about 10 kg of recovered composite pastes 120. Viscosities of individual recovery pastes 119a to 119d are largely varied from about 600 to 800 (Pa·s).
Then, in order to remove fiber pieces 108 formed of a glass fiber having a length of not less than 100 μm and mixed in recovered composite paste 120, filtration using 100-mesh filter 121 is carried out as shown in
Thereafter, the viscosity is adjusted as shown in
The following is a description of a column of the number of printed sheets of 450 (the number of printed sheets in a brand-new product)+200 (the number of printed sheets as a reuse paste)=650 (the total number of printed sheets) in Table 2. Even in a first-time reused reuse conductive paste, a defect does not occur until the number of the printed sheets is 200 when the holes having the diameters of 80 μm to 200 μm are used. In the first-time reused reuse paste, the number of the printed sheets of 200 corresponds to that 650 sheets are actually printed because 450 sheets have already been printed at the time of a brand-new product.
In the case of the hole having the diameter of 80 μm, the defect rate is 63.9 when the number of printed sheets is 450 in Table 1, but the defect rate is 0 when the number of printed sheets is 450+200=650 in Table 2. Thus, in this exemplary embodiment, even when a small diameter of 80 μm in which the defect rate tends to be increased is used and the number of printed sheets is increased, the defect rate can be drastically reduced.
The following is a description of a column of the number of printed sheets 450 (the number of printed sheets in a brand-new product)+400 (the number of printed sheets as a reuse paste)=850 (the total number of printed sheets) in Table 2. In a first-time reused reuse paste, when the number of printed sheets is 400 sheets, the defect rate is 66.7 for the hole having the diameter of 80 μm, 30.6 for the hole having the diameter of 100 μm, 21.3 for the hole having the diameter of 130 μm, 12.5 for the hole having the diameter of 150 μm, and 1.2 for the hole having the diameter of 200 μm. Also in a reused paste, it is shown that as the number of the printed sheets is increased, the defect rate is increased particularly when the diameter of the hole is small.
In Table 2, the viscosity of the reuse paste is adjusted to be not less than 5 (Pa·s) and not more than 50 (Pa·s). When the viscosity of the reuse paste is less than 5 (Pa·s), a solid part is lowered, which may influence the via resistance. Furthermore, when the viscosity is high, the filling property in the via may be influenced. When the initial viscosity of the reuse paste is more than 50 Pa·s, the number of sheets that can be printed thereafter is reduced. Therefore, it is preferable that the viscosity before the start of printing is adjusted to not less than 5 (Pa·s) and not more than 50 (Pa·s). The viscosity of the reuse paste is made to be not less than 5 (Pa·s) and not more than 50 (Pa·s), and furthermore, the solid part thereof is also desirably adjusted to the range of not more than the solid part (for example, not less than 85 wt % and not more than 95 wt %)±1 wt. % of the brand-new conductive paste.
When the hole diameter is less than 130 μm, a defect does not occur when the viscosity of the conductive paste is 100 (Pa·s), but a defect occurs when the viscosity is 125 (Pa·s). Therefore, it is desirable that conductive pastes which have not been filled in the holes should be recovered as a recovery paste when the viscosity of the conductive paste is not less than about 100 (Pa·s). Since the viscosity of the conductive paste before the start of printing of the reuse paste is 20 (Pa·s), conductive pastes which have not been filled in the holes may be recovered as a recovery paste when the viscosity is not less than about 5 times as high as the viscosity before the start of printing of the reuse paste.
When the hole diameter is not less than 130 μm and less than 200 μm, a defect does not occur when the viscosity of the conductive paste is 125 (Pa·s), but a defect occurs when the viscosity is 212 (Pa·s). Therefore, it is desirable that conductive pastes which have not been filled in the holes should be recovered as a recovery paste when the viscosity of the conductive paste is not less than about 120 (Pa·s). Since the viscosity of the conductive paste before the start of printing of the reuse paste is 20 (Pa·s), conductive pastes which have not been filled in the holes may be recovered as a recovery paste when the viscosity is not less than about 6 times as high as the viscosity before the start of printing of the reuse paste.
When the hole diameter is not less than 200 μm, a defect does not occur when the viscosity of the conductive paste is 212 (Pa·s), but a defect occurs when the viscosity is 345 (Pa·s). Therefore, it is desirable that conductive pastes which have not been filled in the holes should be recovered as a recovery paste when the viscosity of the conductive paste is not less than about 200 (Pa·s). Since the viscosity of the conductive paste before the start of printing of the reuse paste is 20 (Pa·s), conductive pastes which have not been filled in the holes may be recovered as a recovery paste when the viscosity is not less than about 10 times as high as the viscosity before the start of printing of the reuse paste.
It may be difficult to precisely obtain measurement values of the viscosity in processes every measurement time. In such a case, it is useful to measure what times the viscosity after printing is as large as a viscosity before start of printing is defined as 1, and to recover the conductive pastes which have not been filled in the hole as a recovery paste. Herein, the viscosity before start of printing is defined as 1, but the viscosity after predetermined number of sheets (for example, ten sheets) are printed may be defined as 1.
Furthermore, as shown in Table 2, relation between the viscosity and the number of printed sheets at which a defect occurs is previously examined, and the conductive pastes which have not been filled in the hole after a predetermined number of sheets are printed may be recovered as the recovery paste.
However, since the results shown in Table 2 are obtained after 450 sheets have already been printed in the brand-new product, it is shown that the number of printed sheets is increased to twice as many as that in Table 1.
The following is a description of a column of the number of printed sheets of 450 (the number of printed sheets in the brand-new product)+450 (the number of printed sheets as the reuse paste)=900 (the total number of printed sheets) in the Table 2. Even with the first-time reused reuse paste, after 450 sheets (900 sheets in total) are printed, the defect rate is increased.
Therefore, the conductive paste with which 900 sheets are printed in total is formed into recovered composite paste 120 as shown in
The following is a description of a column of the number of the printed sheets of 900 (the number of printed sheets in a brand-new product+the number of printed sheets as the first-time reproduced reuse paste)+150 (the number of printed sheets as the second-time reproduced reuse paste)=1050 (the total number of printed sheets) in Table 3. Even with the second-time reused reuse paste, a defect does not occur until the number of printed sheets is 150 when the hole having a diameter of 80 μm to 200 μm is used. The number of the printed sheets of 150 with the second-time reproduced reuse paste corresponds to that 1050 sheets are actually printed because 450 printed sheets are completed at the time of a brand-new product as 450 printed sheets of first-time reproduced reuse paste.
As mentioned above, it is shown that the concoctive pastes with a defect rate generated according to the increase in the number of printed sheets can be repeatedly used for manufacturing a printed circuit board by repeating reproduction processes as shown in
When the hole diameter is smaller than 130 μm, a defect does not occur when the viscosity of the conductive paste is 110 (Pa·s), but a defect occurs when the viscosity is 158 (Pa·s). Therefore, it is desirable that the conductive pastes which have not been filled in the holes should be recovered as a recovery paste when the viscosity of the conductive paste is not less than about 110 (Pa·s). Since the viscosity of the conductive paste before the start of printing of the second-time reused reuse paste is 35 (Pa·s), when the viscosity becomes not less than about three times as high as the viscosity before the start of printing of the second-time reused reuse paste, conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
When the hole diameter is not less than 130 μm and less than 200 μm, a defect does not occur when the viscosity of the conductive paste is 158 (Pa·s), but a defect occurs when the viscosity is 215 (Pa·s). Therefore, it is desirable that the conductive pastes which have not been filled in the holes should be recovered as a recovery paste when the viscosity of the conductive paste is not less than about 150 (Pa·s). Since the viscosity of the conductive paste before the start of printing of the second-time reused reuse paste is 35 (Pa·s), when the viscosity becomes not less than about four times as high as the viscosity before the start of printing of the second-time reused reuse paste, conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
When the hole diameter is not less than 200 μm, a defect does not occur when the viscosity of the conductive paste is 215 (Pa·s), but a defect occurs when the viscosity is 348 (Pa·s). Therefore, it is desirable that the conductive pastes which have not been filled in the holes should be recovered as a recovery paste when the viscosity of the conductive paste is not less than about 210 (Pa·s). Since the viscosity of the conductive paste before the start of printing of the second-time reused reuse paste is 35 (Pa·s), when the viscosity becomes not less than about six times as high as the viscosity before the start of printing of the second-time reused reuse paste, conductive pastes which have not been filled in the holes may be recovered as the recovery paste.
It may be difficult to precisely obtain measurement values of the viscosity in processes every measurement time. In such a case, it is useful to measure what times the viscosity after printing is as large as the viscosity before the start of printing of the second-time reused reuse paste where the viscosity before the start of printing of the second-time reused reuse paste is defined as 1, and to recover the conductive pastes which have not been filled in the hole as a recovery paste. Herein, the viscosity before the start of printing of the second-time reused reuse paste is defined as 1, but the viscosity after predetermined number of sheets (for example, ten sheets) are printed may be defined as 1.
Furthermore, as shown in Table 3, relation between the viscosity and the number of printed sheets at which a defect occurs is previously examined, and the conductive pastes which have not been filled in the hole after a predetermined number of sheets are printed may be recovered as the recovery paste.
Next, a case in which a finer mesh (400 mesh) is used for filter 121 (see
When the mesh is made to be finer, it is possible to enhance the rate of removing fiber pieces 108 or the like mixed in recovered composite paste 120 (see
By combining a plurality of filters 121 having different meshes, clogging can be suppressed. Furthermore, the mesh is not necessarily limited to a net type. Surface-type filtration (surface filtration), depth-type filtration (depth filtration), cake-type filtration (glass fibers accumulated on the surface of the filter is used as a cake, and this cake is used as a filter), or the like, may be used. It is useful that commercially available products are improved for such filtration materials or filtration equipment.
In order to remove fiber pieces 108 mixed in recovered composite paste 120, filtration is carried out by using a 400-mesh filter 121 as shown in
Thereafter, the viscosity is adjusted as shown in
The following is a description of a column of the number of printed sheets of 450 (the number of printed sheets in a brand-new product)+250 (the number of printed sheets as a reuse paste through 400-mesh filtration)=700 (the total number of printed sheets) in the Table 4. A defect does not occur until the number of printed sheets is 250 (the total number of printed sheets of 700) when the hole having the diameter of 80 μm to 200 μm is used. Furthermore, because fine filter 121 having 400 meshes is used for filtration, glass fibers remaining in the reuse paste can be further reduced. Therefore, the increase in the viscosity can be suppressed.
The following is a description of a column of the number of printed sheets of 900 (the number of printed sheets in a brand-new product+at a first-time reproduction)+250 (the number of printed sheets as a reuse paste through 400-mesh filtration)=1150 (the total number of printed sheets) in the Table 5. Even if reproduction is repeated twice, a defect does not occur until the number of printed sheets is 250 (the total number of printed sheets is 1150) when the hole having the diameter of 80 μm to 200 μm is used. Because fine filter 121 having 400 meshes is used for filtration, glass fibers remaining in the reuse paste can be further reduced. Therefore, the increase in the viscosity can be suppressed.
As a curing agent of thermosetting resin, a liquid curing agent of acid anhydride and a catalyst such as imidazole are generally used. However, when a reproduction process is repeated a plurality of times, reaction easily proceeds. Therefore, even if a resin component is supplemented, the viscosity of the reuse paste is extremely higher than the original viscosity. On the contrary, in this exemplary embodiment, a latent curing agent is solid at least from a process of producing conductive paste 105 and applying it to protective film 102 to a process of producing a reuse paste. When a solid latent curing agent is used, the increase in the viscosity can be suppressed, thus enabling stable reuse.
As mentioned above, as shown in this exemplary embodiment, by recycling and further reusing conductive paste 105, waste paste can be reduced.
Furthermore, fiber piece 108 may be fiber piece 108 made of glass constituting first prepreg 101 or second prepreg 125 in many cases. Therefore, an opening diameter of filter 121 used in a filtration process is not less than three times as large as an average particle diameter of metal particles included in the conductive paste, and it is desirable to be as not more than 20 times, furthermore not more than 10 times, and furthermore not more than 5 times as large as an average diameter of the fibers. When the opening diameter of filter 121 is not more than 2 times as large as an average particle diameter of metal particles, clogging of filter 121 easily occurs. Furthermore, when the opening diameter of filter 121 is larger than 30 times as large as an average diameter of fibers, short fiber pieces 108 may not be able to be filtered. The opening diameter of filter 121, the average particle diameter of metal particles, the diameter of fibers, or the like, can be observed and measured by using SEM or the like.
Furthermore, it is desirable that the opening diameter of filter 121 should be not less than two times as large as the particle diameter of the solid latent curing agent. When it is less than two times, the solid latent curing agent may be removed together with a foreign substance and curing of the conductive paste becomes insufficient.
In first prepreg 101 and second prepreg 125, it is useful to differentiate at least one of the thickness of the prepreg itself, or the number or density (weaving method, density, the number of fibers, or the like) of glass fibers or aramid fibers constituting the prepreg. When prepregs having different thicknesses, the numbers or densities of glass fibers or aramid fibers constituting the prepreg are used, various circuit boards can be obtained.
Furthermore, diameters of vias of one prepreg may be one diameter. Alternatively, vias having a plurality of different diameters may be formed in one prepreg.
Note here that in this exemplary embodiment, a protective film in preparing a fiber piece housing paste is referred to as a first protective film, and a protective film in producing a circuit board by using a reuse paste is referred to as second protective film. However, a protective film in preparing a fiber piece housing paste may be referred to as a second protective film, and a protective film in producing a circuit board by using reuse paste may be referred to as a first protective film.
Furthermore, in this exemplary embodiment, a hole formed in the prepreg in preparing the fiber piece housing paste is referred to as a first hole, and a hole formed in the prepreg in producing a circuit board by using the reuse paste is referred to as a second hole. However, a hole formed in the prepreg in preparing the fiber piece housing paste may be referred to as a second hole, and a hole formed in the prepreg in producing the circuit board by using the reuse paste may be referred to as a first hole.
A method of manufacturing a reuse paste in accordance with this exemplary embodiment can reduce fiber pieces to be mixed in a conductive paste in a circuit board using the conductive paste for connecting layers. As a result, yield can be improved. Furthermore, since conductive paste including fiber pieces mixed therein can be reused, a material cost of the circuit board can be radically reduced and an amount of a waste product can be reduced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-163976 | Jul 2011 | JP | national |
This application is a divisional application of U.S. application Ser. No. 13/817,733, filed Feb. 19, 2013, which in turn is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2012/004688, filed on Jul. 24, 2012, which in turn claims the benefit of Japanese Application No. 2011-163976, filed on Jul. 27, 2011, the disclosures of which applications are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13817733 | Feb 2013 | US |
| Child | 13929691 | US |
