Patent Application
20160143150
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-231564, filed Nov. 14, 2014, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate to a method of manufacturing a printed circuit board including a solder resist layer.
In general, a solder resist layer is formed on a surface of a flexible printed circuit board. Such a solder resist layer is conventionally formed through an application process of an insulating material in a liquid form on the entire surface of a substrate using screen printing or the like, a drying process of the insulating material, and a lithography process of the insulating material. It would be desirable to efficiently form such a solder resist layer.
One or more embodiments are directed to provide a method of efficiently forming a solder resist layer.
In general, according to an embodiment, a method for manufacturing a flexible printed circuit module includes discharging an insulating material from an inkjet head towards a surface of a flexible printed circuit board, such that an electrode on the surface of the flexible printed circuit board is exposed, and curing the insulating material to be formed.
Hereinafter, embodiments are described with reference to drawings. In the present disclosure, with respect to some structural elements, a plurality of expressions is used. However, these expressions are merely examples, and each of the above-mentioned structural elements may be expressed in other ways. Further, the structural elements which are expressed in a single way may be expressed in plural ways.
The drawings are schematic views, and hence the relationship between thicknesses and planar sizes, a ratio of thicknesses of the respective layers and the like may not be equal to those of a real product. The relationship or the ratio between sizes of the components may differ between drawings.
As shown in
The module 4 according to the present embodiment is a camera module, for example. Accordingly, one example of the electronic component 12 is a camera. The module 4 is not limited to the above-mentioned example, and various modules may suitably be employed as the module 4. That is, the electronic component 12 mounted on the printed circuit board 11 is not limited to a camera and, broadly, various components may be mounted on the printed circuit board 11 as the module 4.
Next, the printed circuit board 11 is described in detail.
As shown in
The first wiring portion 22 extends between the terminal portion 21 and the first component mounting portion 24 so as to electrically connect the terminal portion 21 and the first component mounting portion 24. The second wiring portion 23 extends between the first component mounting portion 24 and the second component mounting portion 25 so as to electrically connect the first component mounting portion 24 and the second component mounting portion 25. Each one of these wiring portions 22, 23 includes a flexible base film made of polyimide or the like, a wiring pattern formed on the base film, and a cover lay film which covers the wiring pattern. These wiring portions 22, 23 have flexibility.
Each one of the first and second component mounting portions 24, 25 includes pads 32 (mounting pads) exposed on a surface of the printed circuit board 11, and the electronic component 12 is mountable on the pads 32. The pads 32 are also referred to as, for example, electrodes. The first component mounting portion 24 and the second component mounting portion 25 have the same structure and the same functions although the first component mounting portion 24 and the second component mounting portion 25 differ from each other in size and type of components to be mounted thereon. Accordingly, the first component mounting portion 24 is described in detail hereinafter as a representative mounting portion.
The pads 32 are exposed on the surface of the substrate 31. That is, the pads 32 are exposed to the outside of the printed circuit board 11, and connecting portions 39 (solder balls, for example) of the electronic component 12 are connected to the pads 32. By connecting the connecting portions 39 to the pads 32, the electronic component 12 is mounted on the pads 32, and is electrically connected to the printed circuit board 11. The surface layer pattern 33 (conductor pattern, wiring pattern) includes a plurality of lines 33a, 33b, and is formed on a surface of the substrate 31. The plurality of lines 33a, 33b may be signal lines or power source lines.
As shown in
According to such a structure, the solder resist 34 includes opening portions 41 corresponding to the pads 32 (opening portions 41 for exposing the pads 32 to the outside). On the other hand, the solder resist 34 covers the surface layer pattern 33 (lines 33a, 33b).
The solder resist 34 is formed on the component mounting portion 24 so as to cover the whole region of the component mounting portion 24 except for the pads 32. The solder resist 34 is made of an insulation material so that the solder resist 34 electrically insulates the plurality of pads 32 from each other, and electrically insulates the plurality of lines 33a, 33b from each other. The solder resist 34 is provided so that a solder is not formed on portions other than contact portions for electric connection at the time of mounting the electronic component 12 on the printed circuit board 11 thus causing short-circuiting. The solder resist 34 also protects the printed circuit board 11 from an ambient environment such as dust, heat, or moisture, thus enhancing long-term reliability of the printed circuit board 11.
Next, a method of manufacturing the printed circuit board 11 according to the present embodiment is described.
As shown in
To be more specific, first, pretreatment such as cleaning is carried out on the surface of the substrate 31. Next, a detection mark (alignment mark) formed on the individual substrate 31, for example, is read by a device, an expansion and contraction state (thermally expanded state) of the substrate 31 caused by an ambient environment is detected based on the position of the mark, and a position where a solder resist material is to be applied by coating is individually adjusted in accordance with the expansion and contraction state of the substrate 31.
Next, a solder resist material 43 having a fluidity (in a liquid state, for example) is applied on portions of the surface of the substrate 31 using an inkjet method such that the solder resist material 43 is not formed on at least the center portion of each pad 32. That is, the solder resist material 43 is discharged from an inkjet head H of the inkjet device M and is supplied to a position where the solder resist 34 is expected to be formed using an inkjet device M ((b) in
Next, heat is applied to the primarily-cured solder resist material 43 thus thermally curing the solder resist material 43 ((c) in
According to the above-mentioned method of forming a solder resist 34, various advantageous effects described hereinafter may be acquired. First, for a comparison purpose, a method of forming opening portions in the solder resist which correspond to pads by punching using a die is considered as a comparative method. In this case, when miniaturized electronic components which have been employed recently are mounted on a printed circuit board at a narrow pitch, the formation of such openings in extremely minute portions would be difficult when the punching of the die is employed.
Also, a method of forming a solder resist using a photosensitive material is considered as another comparative method. In this case, to form a solder resist, steps such as pretreatment, printing, drying, exposing, developing, peeling and thermal curing, and the like of a solder resist material would be necessary so that a manufacturing process would be long. Further, according to this method, even when a solder resist is formed on a surface of a substrate, first, the solder resist material is applied to the whole surface of the base member by screen printing or the like, and thereafter unnecessary solder resist portions are removed. Accordingly, an amount of the solder resist material which may be wasted is not small.
Further, according to the method of forming a solder resist using a photosensitive material, a scum (a residue of the solder resist material which cannot be removed in a peeling step) may remain on the pad and the remaining scum may adversely affect the formation of electroless Ni—Au plating and the soldering, which are succeeding steps. Accordingly a step of cleaning surfaces of the pads by plasma treatment or the like may be necessary after the above-mentioned peeling step.
Further, the flexible printed circuit board exhibits the larger expansion and contraction caused by change of the ambient temperature or the like, relative to a rigid wiring board. Accordingly, for example, when an exposure film is used, a size of the exposure film may not match a size of the flexible printed circuit board. Accordingly, accuracy of the positioning of the solder resist with respect to the pads may be affected by the expansion and contraction of the flexible printed circuit board.
On the other hand, according to the present embodiment, the solder resist 34 is formed as follows. That is, the solder resist material 43 is applied on portions of the surface of the substrate 31 on which the pads 32 are mounted using an inkjet method such that the solder resist material 43 is not formed on at least a center portion of each pad 32, and the solder resist material 43 is cured.
According to such a method, first, a process for forming the solder resist 34 may be largely shortened. That is, by adopting the inkjet method, the solder resist 34 may be formed through the steps including pretreatment, coating using an inkjet method, UV-curing, and thermal curing. Such a method can be performed in a shorter time period than a method of forming a solder resist which necessitates steps such as exposing, developing, and a peeling. Accordingly, it is possible to reduce a material cost and a labor cost.
Further, according to the method of forming a solder resist using an inkjet method, the solder resist material 43 is applied only to necessary portions on the surface of the substrate 31. Accordingly, compared to a method where a solder resist material is applied to the whole surface of the substrate 31, amount of wasted solder resist material is small. Accordingly, it is possible to efficiently use the solder resist material.
According to the method of forming a solder resist using an inkjet method, the solder resist material 43 is applied by only to necessary portions, so that a scum or the like does not remain on the pads 32. As a result, even when any particular post-treatment is not performed, the formation of electroless Ni—Au plating and soldering may be favorably performed. Accordingly, reliability of the printed circuit board 11 may be improved while shortening the manufacturing process.
With respect to the positional accuracy of the solder resist 34 with respect to the pads 32, by adopting the inkjet method, the position where the solder resist material 43 is applied may be adjusted so as to conform to positions of the pads 32 on the individual printed circuit boards 11. That is, for example, an amount of expansion and contraction of the individual printed circuit board 11 is detected using a detection mark or the like, and the position where the solder resist material 43 is applied may be individually adjusted based on the amount of expansion and contraction of the printed circuit board 11. Accordingly, the positional accuracy of the solder resist 34 with respect to the pads 32 may be acquired more easily compared to the case where an exposure film is used. In other words, according to the method of forming the solder resist using an inkjet method, the positional accuracy of the solder resist is minimally affected by the expansion and contraction of the flexible printed circuit board caused by changes of an ambient temperature.
According to the method of forming the solder resist using an inkjet method, an exposure mask and a printing plate are unnecessary. Accordingly, a material cost may be reduced. Further, the method may easily achieve the production of many kinds in small quantities.
Next, the second to seventh embodiments are described. According to the second to seventh embodiments, the shape and the structure of the solder resist 34 are modified from the ones according to the first embodiment, considering the advantageous effects acquired by forming the solder resist 34 by an inkjet method. The structural components of the second to seventh embodiments which have functions identical with or similar to the structural components of the first embodiment are depicted with the same symbols, and the repeated explanation of these structural components is omitted. The structures of the second to seventh embodiments other than the structures described hereinafter are same as the corresponding structures of the first embodiment.
To describe the present embodiment in detail, the solder resist 34 has first portions 51 and second portions 52. The first portions 51 are formed in regions which do not correspond to surface layer patterns 33 in the thickness direction of a substrate 31, and are in contact with portions of a surface of the substrate 31 where the surface layer patterns 33 are not formed. The second portions 52 are formed in regions which correspond to the surface layer patterns 33 in the thickness direction of the substrate 31, and overlap peripheral portions 32a of pads 32 or lines 33a, 33b.
As shown in
By adopting the inkjet method, a coating amount of the solder resist material 43 may be changed depending on positions. Accordingly, the presence or the non-presence of the surface layer pattern 33 is first determined, and then a coating amount of the solder resist material 43 is increased at portions (first portions 51) where the surface layer pattern 33 is not present and the coating amount of the solder resist material 43 is decreased at portions (second portions 52) where the surface layer pattern 33 is present. According to such distribution of the thickness, a surface of the whole solder resist 34 may become smooth.
It may be also possible to acquire a solder resist having a smooth surface by laminating an insulating raw film material on a surface of a substrate, for example. However, such a raw film material is generally expensive, and hence a manufacturing cost of a printed circuit board may be high. On the other hand, when the solder resist 34 is formed using an inkjet method as in the case of the present embodiment, the solder resist 34 having a smooth surface may be formed without using an expensive raw film material.
To describe the present embodiment in detail, a surface layer pattern 33 of the printed circuit board 11 includes first lines 71a, 71b, 71c and second lines 72a, 72b. The first lines 71a, 71b, 71c configure general signal lines or power source lines, for example. The second lines 72a, 72b configure signal lines through which high-speed signals (signals having higher frequency) flow compared to the first lines 71a, 71b, 71c. One example of the second lines 72a, 72b is microstrip lines which configure high-speed transmission lines. The second lines 72a, 72b may be signal lines through which high-speed signals conforming to the PCI Express standard flow, or other signal lines, for example.
As shown in
According to the above-mentioned structure, the present embodiment may achieve various advantageous effects substantially equal to the advantageous effects of the first embodiment and, at the same time, a transmission speed of the printed circuit board 11 may be improved and a transfer loss may be reduced. According to the studies carried out by the inventors of the present disclosure, it is found that, with respect to signal line through which high-speed signals flows, the lower an effective dielectric constant, the more electric characteristics of the high-speed signals is improved. Accordingly, the signal lines having a low effective dielectric constant are advantageous in view of improving a transmission speed and reducing a transfer loss. According to the studies carried out by the inventors of the present disclosure, it is also found that when a solder resist is formed on the signal lines, an effective dielectric constant of the signal lines is increased.
In view of the above, in the present embodiment, the thickness of the first portion 73 of the solder resist 34 and the thickness of the second portion 74 of the solder resist 34 are different from each other. That is, the first portion 73 of the solder resist 34 which covers the first lines 71a, 71b, 71c is formed with a normal thickness, for example, and the second portion 74 of the solder resist 34 which covers the second lines 72a, 72b is formed with a thickness smaller than the thickness of the first portion 71. Due to such a structure, an influence of an ambient environment (air layer) on the second lines 72a, 72b is increased, and hence an effective dielectric constant of the second lines 72a, 72b may be lowered. Accordingly, an electric characteristic of the second lines 72a, 72b is improved so that a transmission speed of the printed circuit board 11 may be improved, and a transfer loss may be reduced.
To describe the present embodiment in detail, a surface layer pattern 33 of the printed circuit board 11 includes first lines 71a, 71b, 71c, and second lines 72a, 72b. The details of the first lines 71a, 71b, 71c and the second lines 72a, 72b are substantially the same as the corresponding lines in the third embodiment.
As shown in
According to the above-mentioned structure, the fourth embodiment may achieve various advantageous effects substantially the same as the advantageous effects of the first and second embodiments. At the same time, in the same manner as the third embodiment, a transmission speed of the printed circuit board 11 may be improved, and a transfer loss may be reduced. That is, in the present embodiment, the first portion 73 of the solder resist 34 and the second portion 74 of the solder resist 34 are formed using different materials (different kinds of materials). That is, the first portion 73 of the solder resist 34 which covers the first lines 71a, 71b, 71c is formed using a first material, while the second portion 74 of the solder resist 34 which covers the second lines 72a, 72b is formed using a second material having a smaller dielectric constant than the first material, by changing a solder resist material to be applied. According to such a structure, an effective dielectric constant of the second lines 72a, 72b may be lowered. Accordingly, an electric characteristic of the second lines 72a, 72b is improved so that a transmission speed of the printed circuit board 11 is improved and a transfer loss is reduced.
A material having a small dielectric constant is expensive in general. That is, according to the present embodiment, an expensive material is used only for forming portions where the use of the expensive material is effective in view of a transmission speed. Accordingly, a transmission speed of the printed circuit board 11 may be improved and a transfer loss may be reduced while suppressing the amount of the expensive material as a whole.
To describe the present embodiment in detail, an electronic component 12 according to the present embodiment is a light emitting component, for example, and includes a light emitting element 81 (semiconductor element), a light-transmissive portion 82, electrodes 83a, 83b, and a mold resin 84. The light emitting element 81 includes a plurality of clad layers and active layers interposed between these clad layers, respectively. The light emitting element 81 includes an InGaN layer which emits blue light, for example.
The light transmissive portion 82 covers the light emitting element 81. One example of the light transmissive portion 82 is a phosphor layer, and the phosphor layer is made of a resin where phosphor particles which convert blue light into long-wavelength light are dispersed. The light transmissive portion 82 may be formed of a colorless transparent layer or the like.
The electrodes 83a, 83b are posts made of metal (copper, for example) and project from the light emitting element 81. The electrodes 83a, 83b are connected to pads 32 of the printed circuit board 11 with a bonding material 85 such as solder (cream solder). The electrodes 83a, 83b supply electricity to the light emitting element 81. The mold resin 84 covers peripheral surfaces of the electrodes 83a, 83b.
As shown in
The second portion 87 is formed outside the first portion 86, and is located away from the light emitting element 81 than the first portion 86 is. The second portion 87 is formed of an inexpensive material having low light reflectance compared to a material of the first portion 86.
According to the above-mentioned structure, the fifth embodiment may achieve various advantageous effects substantially equal to the advantageous effects of the first and second embodiments and, at the same time, the fifth embodiment may provide a module 4 where irradiation efficiency of the electronic component 12 is improved. That is, in the present embodiment, the first portion 86 of the solder resist 34 and the second portion 87 are formed using different materials (different kinds of materials). In other words, the first portion 86 of the solder resist 34 positioned around the electronic component 12 is formed using a first material having relatively high light reflectance, while the second portion 87 which receives a smaller amount of light from the electronic component 12 compared to the first portion 86 is formed using a material having lower light reflectance than the first portion 86. According to such a structure, the fifth embodiment may provide the module 4 where irradiation efficiency of the electronic component 12 is improved.
A material having a color, such as white, of high light reflectance, for example, is generally expensive. That is, according to the present embodiment, an expensive material is used only for portions that contribute to improve irradiation efficiency. Accordingly, the fifth embodiment may provide the module 4 where irradiation efficiency is improved while suppressing an amount of an expensive material as a whole.
To describe the present embodiment in detail, the module 4 according to the present embodiment includes an electronic component 12. The electronic component 12 is fixed to a surface of the solder resist 34 with an adhesive portion 92. The adhesive portion 92 is formed of an adhesive sheet or an adhesive agent, for example. Bonding wires 93 are provided between the electronic component 12 and the pads 32. The electronic component 12 is electrically connected to the pads 32 through the bonding wires 93. The electronic component 12 may be connected to pads 32 of a printed circuit board 11 by soldering.
As shown in
As shown in
According to the above-mentioned structure, the sixth embodiment may achieve various advantageous effects substantially equal to the advantageous effects of the first embodiment and, at the same time, the sixth embodiment may improve packing density of the printed circuit board 11 while maintaining reliability of the printed circuit board 11. That is, the projecting portions 91 which block a resin material for forming the resin portions 94 are formed by making portions of the solder resist 34 have a larger thickness. Accordingly, even when an amount of resin material sufficient to cover the electronic component 12 and the bonding wires 93 is supplied, it is possible to retain the resin material within an area surrounded by the projecting portion 91. Accordingly, areas on the surface of the printed circuit board 11 which are occupied by the resin portions 94 may be decreased. According to such a structure, the sixth embodiment may improve packing density of the printed circuit board 11 while improve reliability of the printed circuit board 11.
The semiconductor devices 101 may be used in a state where the semiconductor devices 101 are mounted on a host device 102 such as a server, for example. The host device 102 includes a plurality of connectors 103 (slots, for example). The plurality of semiconductor devices 101 are mounted on the connectors 103 of the host device 102, respectively. The semiconductor device 101 includes a printed circuit board 11, a semiconductor package 104 mounted on the printed circuit board 11, and a plurality of electronic components 105 mounted on the printed circuit board 11. The semiconductor package 104 includes a plurality of semiconductor elements and a mold resin which integrally covers these semiconductor elements, for example.
The printed circuit board 11 includes a plurality of pads 32 on which the semiconductor package 104 and the electronic component 105 are mounted and a solder resist 34 which is formed such that at least center portions of the respective pads 32 is exposed. The solder resist 34 is formed using an inkjet method, and has the same structure as the solder resist according to any one of the first to sixth embodiments. The semiconductor device 101 having such a structure may also achieve various advantageous effects substantially equal to the advantageous effects of the first to sixth embodiments.
Although the first to seventh embodiments are described heretofore, the embodiments are not limited to the above-mentioned examples. For example, the above-mentioned respective embodiments are also applicable to a method of forming a solder resist of a rigid printed circuit board.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-231564 | Nov 2014 | JP | national |
