Patent Application
20140231007
(1) Field of the Invention This invention concerns ultrathin copper clad laminates useful in manufacturing printed circuit boards comprising a thin woven glass sheet laminated between two opposing layers of copper foils as well as to methods for their manufacture.
(2) Description of the Prior Art
As electronic devices become smaller, the components that make up the devices also grow smaller. At the same time the component performance demands increase. As the component sizes and electronic device sizes decrease, there is a need for similar decreases in the thickness of the circuit boards that carry the components. However, as circuit board laminates decrease in thickness, it becomes more difficult to keep the thickness of the board constant across its surface area. Additionally, the thinner circuit boards get, the more difficult it is to manufacture laminates used in printed circuit boards that consistently meet the electronic requirements of the circuit board industry. As a result, there is a continuing need for very thin circuit board laminate materials as well as for methods for making thin circuit board laminates consistently and reproducibly.
One aspect of this invention is A laminate comprising the combination of a base laminate including resin impregnated fabric sheet material having a first planar surface, a second planar surface, the fabric sheet having an original thickness of from about 10 to about 30 microns and at least one copper foil sheet that is adhered to a planar surface of the fabric sheet material by a cured resin wherein the base laminate thickness is from about 1.0 to about 1.75 mils (25-45 microns).
In optional embodiments, the laminate may include a copper foil sheet is adhered to each of the fabric sheet material first and second surfaces. The laminate may further optionally have an average minimum dielectric thickness of no less than about 0.75 mils and an average maximum thickness no greater than about 1.5 mils (19-38 microns) or alternatively an average minimum dielectric thickness of no less than about 0.8 mils and an average maximum thickness no greater than about 1.2 mils (20-30 microns).
The laminate copper foil may have a thickness of from about 15 to about 40 microns or alternatively a thickness of from about 15 to about 25 microns.
The base laminate may have additional useful properties. For example, the base laminate thickness preferably will differ by no more than 20% when measured at the center and each of four corners of an 18 inch by 24 inch rectangular laminate sheet.
The laminate resin may also include several optional features. In one embodiment the resin will include essentially no fillers. In addition to including no fillers the resin can include a replacement flow control agent such as a phenoxy resin which may be present in the resin in an amount ranging from more than 0 wt. % to about 2 wt. % on a dry resin basis.
In a further embodiment, the fabric material is a woven glass fabric that optionally has no more than 2 glass filaments stacked over and under wherein the glass filaments have a diameter of from about 3 microns to about 5 microns or a filament diameter of about 4 microns.
Another aspect of this invention is a laminate comprising the combination of: (i) a base laminate including a resin impregnated woven glass fabric having a first planar surface, a second planar; and (ii) a copper foil sheet adhered to each of the first and second base laminate planar surfaces by the cured resin wherein the laminate has an average minimum dielectric thickness of no less than about 80 mils and an average maximum thickness of no greater than about 1.2 mils (20-30 microns) wherein the woven glass fabric has no more than 2 glass filaments stacked over and under. In this or all embodiments, the resin may have a Tg of 180-200 ° C.
Still another aspect of this invention is a method for manufacturing an ultrathin laminate material comprising the steps of: (i) placing a first copper foil sheet having into contact with a first planar surface of a fabric sheet having a thickness of from 10 to about 30 microns wherein the fabric sheet is impregnated with a resin or a layer of resin lies between the first copper foil sheet and the fabric sheet first planar surface or both; and (ii) applying pressure and heat to the stacked material for a time sufficient to essentially fully cure the resin to form a laminate sheet having a base laminate thickness of from about 1.0 to about 1.75 mils (25-45 microns.
In one embodiment of this invention aspect, a second copper sheet is placed into contact with a second planar surface of the fabric sheet before applying pressure and heat to the stacked material wherein the fabric sheet is impregnated with a resin or a layer of resin lies between the second copper foil sheet and the fabric sheet second planar surface or both. In addition, the copper foil may include a b-staged resin layer wherein the b-staged resin has a gel-time of 40-50 seconds and a viscosity of 15-25 Pascal seconds.
In other embodiments, the laminate will have an average minimum dielectric thickness of no less than about 80 mils and an average maximum dielectric thickness of no greater than about 1.2 mils (20-30 microns). Additionally, the fabric sheet may be a woven glass fabric sheet and the fabric sheet may be impregnated with a resin before the resin impregnated fabric sheet is placed into contact with a first copper foil sheet and a second copper foil sheet. Additionally, the fabric sheet may be pre-wetted before impregnating the fabric sheet with a resin
In still another aspect, this invention is a method for manufacturing an ultrathin laminate material comprising the steps of: (i) placing a first copper foil sheet having into contact with a first planar surface of a woven glass fabric sheet having a thickness of from 10 to about 30 microns wherein the fabric sheet is impregnated with a resin or a layer of resin lies between the first copper foil sheet and the fabric sheet first planar surface or both; and (ii) applying pressure and heat to the stacked material for a time sufficient to essentially fully cure the resin to form a laminate sheet having a minimum dielectric thickness of no less than about 0.80 mils and an average maximum dielectric thickness of no greater than about 1.2 mils (20-30 microns).
The present invention relates to ultrathin copper clad laminates that include a thin woven fiber layer associated with one or two layers of resin coated copper. The laminates include a woven fabric sheet layer having a first surface and a second surface and a thin copper sheet adhered to one or both of the first and second woven fabric sheet surfaces by a resin material. The total “base laminate thickness”—the thickness of the core resin impregnated woven fabric layer of the ultrathin copper clad laminate measured with a mechanical device such as a micrometer after removing the copper layer(s) from the laminate—will be from about 1.0 to about 1.75 mils (25-45 microns) and preferably from about 1.3 to about 1.75 mils (33-45 microns).
The ultrathin laminates of this invention are formed using one or two sheets of b-staged resin coated copper and a woven fabric sheet. Alternatively, the laminates are made using one or two sheet of copper and a resin impregnated woven fabric sheet. The laminates can be made using batch or continuous lamination processes. When a b-staged resin coated copper sheets are used, the laminates of this invention are made by placing the resin side of each resin coated copper sheet against opposing planar surfaces of a thin fabric sheet to form a layup and thereafter applying pressure and/or heat to the layup. The pressure and/or heat applied to the layup causes the resin associated with the resin coated copper layer to soften and penetrate into the thin woven fabric sheet and, at the same time, the applied pressure and heat causes the resin to completely cure to form a thin c-staged copper clad laminate.
In an alternative process, the woven fabric sheet is thoroughly impregnated with a resin and the resin is partially cured to a prepreg or b-stage. Copper foil sheets are then applied to one or both planar surfaces of the partially cured resin impregnated woven fabric sheet to form a layup and the layup is fully cured by subjecting the layup to heat and/or pressure as above.
In order to aid in the impregnation of the fabric sheet with the resin, the fabric sheet can be pretreated or pre-wetted with a liquid such as a resin solvent or an uncured or partially cured epoxy resin solution. If a resin solution is used to pre-wet the fabric sheet, then the resin solution will usually have a solids content that is less than the solids content of the resin that is used to impregnate the fabric sheet. For example, the pre-wetting resin can have a solids content of from greater than 0% to about 50% or more. In one embodiment, the fabric sheet is pre-wetted with an epoxy resin solution that includes from about 5 wt. % to about 25 wt. % solids and the remainder solvent.
The ultrathin laminates of this invention may be in the form of copper clad laminates including a copper foil layer attached to each planar surface of the ultrathin base laminate. Alternatively, one or both of the copper foil layers can be partially or totally etched or otherwise removed from one or both planar surfaces of the ultrathin base laminate to form an ultrathin dielectric laminate material layer.
Referring now to
The unassembled laminated materials are then associated with each other to form a layup and thereafter subjected to heat and/or pressure sufficient to cause the resin to flow and impregnate fabric layer (10).
The fabric layer (10) may be any fabric material that has a thickness that is preferably less than about 1 mil (about 25 microns). More preferably fabric layer (10) will have a thickness that is less than about 1 mils (about 25 microns) but greater than about 0.5 mils (about 13 microns). In another embodiment, the fabric layer is a woven glass cloth layer. Some examples of useful woven glass cloth materials include, but are not limited to 101, 104 and 106 glass cloth layers. Also useful are 1000 and 1017 woven glass cloth sheets or rolls such as those manufactured by Nittobo of Tokyo Japan. Properties of several useful woven glass fabric sheet materials are reported in Table 1 below.
1017 woven glass fabrics the high density version of 1000 woven glass fabric in that is has additional filaments per unit of measure in the warp and weft directions. Both 1000 and 1017 woven glass fabrics offer greater mechanical stability to the laminate in comparison to 101 woven glass fabric. Also, both 1000 and 1017 woven glass fabrics are about 60% flatter than 101 woven glass fabric. Moreover, in both 1000 and 1017 woven glass fabrics, the yarns in warp and fill are spread apart so that a maximum of 2 filaments are stacked over and under as shown in
The resin coated copper foil sheets used in certain embodiments of the present invention may be any partially cured resin coated copper sheet materials used in the art. In one embodiment, the resin coated copper foil is a b-staged resin coated copper foil sheet. In order to produce an ultrathin laminate sheet, it is preferred that the resin coated copper foil have a very thin partially cured resin layer and a very thin copper foil layer. Thus, in one embodiment, the resin layer of the resin coated copper can have a thickness that is less than about 50 microns and greater than about 5 microns. In another embodiment, the resin layer can have a thickness of 25 microns or less and 8 microns or greater. In still another embodiment, the resin layer can have a thickness of about 15 microns.
The copper foil sheets used in manufacturing ultrathin laminates of this invention are preferably thin copper foil sheets or rolls such as a copper foil that is 2 oz or less and more preferably 1 oz copper or less. Generally the copper foil will have a thickness of from about 15 to about 40 microns. A narrower and useful copper foil thickness range is from about 15 to about 25 microns. In addition, the copper foil can be regular or reverse treated copper foil. In one embodiment, the copper foil surface that is associated with the resin layer or that is associated with the resin impregnated fabric sheet planar surface will have a roughness of from about 3 to about 5 microns. Alternatively, the copper can be applied in a very thin layer to a prepreg or b-staged base material or to a very thin prepreg or b-staged resin sheet by sputtering, by chemical vapor deposition or by any other process that is known in the art to be useful in applying a very thin layer of metal to a substrate.
Preferred ultrathin laminates of this invention will have an average (measured at 4 or more points of a 18 inch×24 inch laminate sheet) “dielectric thickness” range of from about 0.75 to 1.5 mils (19-38 microns) and more preferably from about 0.8 to about 1.2 mils (20-30 microns). The term “dielectric thickness” refers to the range between the measured minimum and maximum thicknesses of the resin impregnated woven fabric material portion of the laminate and does not include the thickness of any copper layer associated with the laminate. The ultrathin laminate dielectric thickness ranges are measured by preparing a micro cross-section of the laminate and then measuring the minimum and maximum widths of the dielectric portion of the laminate under a microscope. The determination of the minimum dielectric thickness is explained with reference to
Another property of the ultrathin laminates of this invention that can be important is the laminate thickness distribution. Ideally the laminate should have the same thickness measured at any point over the surface area of the laminate. However, in practice, a uniform distribution is nearly impossible to achieve. The more the thickness deviates over the surface area of the laminated, the more likely it is that the laminate will not pass quality control testing such as Hipot testing, peel strength testing, etc. . . . Therefore, in one embodiment, the dimensional stability of the laminates of this invention will be such that the laminate “base thickness” as measured at the center and at the four corners of a 18 inch×24 inch rectangular laminate material will vary no more than about 20% and more preferably no more than about 10%.
The laminates of this invention employ resins to provide a dielectric barrier and/or to strengthen the fabric material layer. The term “resin” is used in the context of this application to refer generally to any curable resin composition that can be used now or in the future in the production of laminates used in printed circuit boards and other electronic applications. Most often, epoxy resins are used to make such laminates. The term “epoxy resin” refers generally to a curable composition of oxirane ring-containing compounds as described in C.A. May, Epoxy Resins, 2nd Edition, (New York & Basle: Marcel Dekker Inc.), 1988.
One or more epoxy resins are added to a resin composition in order to provide the desired basic mechanical and thermal properties of the cured resin and laminates made there from. Useful epoxy resins are those that are known to one of skill in the art to be useful in resin compositions useful for electronic composites and laminates.
Examples of epoxy resins include phenol types such as those based on the diglycidyl ether of bisphenol A (“Bis-A epoxy resin”), on polyglycidyl ethers of phenol-formaldehyde novolac or cresol-formaldehyde novolac, on the triglycidyl ether of tris(p-hydroxyphenol)methane, or on the tetraglycidyl ether of tetraphenylethane, or types such as those based on tetraglycidylmethylenedianiline or on the triglycidyl ether of p-aminoglycol; cycloaliphatic types such as those based on 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexane carboxylate. The term “epoxy resin” also includes within its scope reaction products of compounds containing an excess of epoxy (for instance, of the aforementioned types) and aromatic dihydroxy compounds. These compounds may be halogen substituted.
The resin systems used in the resin coated copper foils may include additives and excipients know to those skilled in the art of formulating resin laminates such as flame retardants. However, it is preferred that the resins used in the laminates of this invention do not include any fillers such as talc, PTFE and so forth. Since fillers are sometimes added to resin systems as flow control agents, it can be useful to include a non-filler flow control agent to the resin before it is applied to a copper foil layer or used to impregnate the fabric cloth layer directly. One useful class of flow control agents are phenoxy resins which can be added to the resin systems used in this invention in amounts ranging from more than 0 wt. % to about 2% on a solids basis.
Some examples of epoxy resins useful in the manufacture of the laminates of this invention are disclosed, for example in U.S. Pat. Nos. 5,464,658, 6,187,852, 6,509,414 and 6,322,885, the specifications of each of which are incorporated herein by reference.
Especially useful epoxy resins will have a cured Tg of from about 180 to 200° C. Moreover the resin and copper when combined and cured should result in a ultrathin laminate that has a peel strength of about 4.5 lb./in or greater. In addition, a resin associated with a copper foil layer prior to the application of the resin coated copper foil layer to a fabric material layer may be b-staged so that the gel time and viscosity of the resin are matched such that the resin penetrates the woven glass fabric and cures quickly during the laminate fabrication process. In one embodiment, the resin is selected and b-staged such that it has a gel time of from 30 to 90 seconds and a viscosity of 5-40 Pascal seconds. In another embodiment, the resin is chosen and b-staged such that it has a gel time of from 40-50 seconds and a viscosity of from about 15-25 Pascal seconds.
In one embodiment, a resin coated copper sheet useful in manufacturing ultrathin laminates of this invention can be made by applying an uncured or partially cured liquid resin to a copper foil sheet wherein the resin layer has a thickness of from about 8 microns to about 20 microns and more preferably a thickness of from about 10 to 15 microns. When a resin coated copper sheet is used to make a laminate having a thickness of about 1 mil or less, the copper foil used will be a 1 oz copper foil having a thickness of about 18 microns and a surface roughness of about 3 microns. The resin will be applied to one surface of the copper sheet at a thickness of about 14 microns and partially cured to form a b-staged resin coated copper sheet.
The resins, fabrics and resin coated copper foil sheets described above can be used to make laminates of this invention in batch or in continuous processes. In exemplary continuous process for manufacturing laminates of this invention, a continuous sheet in the form of each of copper, a resin prepreg and a thin fabric sheet are continuously unwound into a series of drive rolls to form a layered web of fabric, adjacent to the resin prepreg sheet which is adjacent to a copper foil sheet such that the prepreg sheet lies between the copper foil sheet and the fabric sheet The web is then subjected to heat and pressure conditions for a time that is sufficient to cause the resin to migrate into the fabric material and to completely cure the resin. In the resulting laminate, the migration of the resin material into the fabric causes the thickness of the resin layer (the distance between the copper foil material and the fabric sheet material to diminish and approach zero as combination layers discussed above transforms from a web of three layers into a single laminate sheet. In an alternative to this method, a single prepreg resin sheet can be applied to one side of the fabric material layer and the combination sandwiched between two copper layers after which heat and/or pressure is applied to the layup to cause the resin material to flow and thoroughly impregnate the fabric layer and cause both copper foil layers to adhere to the base laminate.
In an alternative embodiment, the resin coated copper sheets can be made at the same time the laminate is being made by applying a thin coating of resin to two different continuously moving copper sheets, removing any excess resin from the sheets to control the resin thickness and then partially curing the resin under heat and/or pressure conditions to form a sheet of b-staged resin coated copper. The sheet(s) of b-staged resin coated copper can then be used directly in the laminate manufacturing process.
In still another embodiment, the fabric material—with or without prior pretreatment—can be continuously fed into a resin bath such that the fabric material becomes impregnated with the resin. The resin can be optionally partially cured at this stage in the process. Next, one or two copper foil layers can be associated with the first and/ or second planar surface of the resin impregnated fabric sheet to form a web after which heat and/or pressure is applied to the web to fully cure the resin.
In yet another embodiment of a continuous process for manufacturing laminates of this invention is shown in
As noted above, the ultrathin laminates of the invention can be made by batch processes as well. In one batch process embodiment, a fabric sheet is applied to the resin layer of a b-staged resin coated copper foil sheet and a second b-staged resin coated copper foil sheet can then be applied—resin layer down—against the exposed fabric sheet. This process can be repeated one or more times to produce a stack including multiple laminates. The stack is them placed in a press that applies pressure and heat to the layup to cure the b-staged resin and to force the resin to flow into the fabric material as it cures. The pressure and heat are removed and the laminates are separated from one another.
The lamination methods and parameters used to manufacture the ultrathin laminates of this invention may vary widely, and are generally well known to the person of ordinary skill in the art. In a typical batch cure cycle, the stack is maintained at a pressure of about 40 psi to about 900 psi and under a vacuum of about 30 in/Hg. The stack temperature is raised from about 180° F. to about 375° F. over a period of about 20 minutes. The stack remains at a temperature of about 375° F. for 75 minutes after which the stack is cooled from a temperature of 375° F. to a temperature to 75° F. over a 20 minute period.
The following examples are illustrative of various aspects of the invention but do not serve to limit its scope.
In this example, a resin system useful for manufacturing ultrathin resin systems of the present invention. The resin system has the following recipe.
The resin is prepared by adding propylene glycol methyl ether into a mixing vessel and then adding all remaining ingredients except for 2-Phenylimidazole into the same mixing vessel and mixing the ingredients for 30 minutes. The 2-Phenylimidazole is dissolved in Propylene glycol methyl ether and then added to the mix. The mixture is homogenized for 30 minutes and the resin is ready to use.
One method for making ultrathin laminates of this invention is by a batch lay up process using a hydraulic press. According to this method, an ultrathin fabric material is placed between two sheets of resin coated copper such that the resin coating contacts the fabric sheet material to form a layup. The layup is placed in a hydraulic press at a pressure of 15-20 bars and at a starting temperature of 110° C. (230° F.). The press temperature is increased to 190° C. (375 ° F.) at a rate of 5-7 degrees C. per minute. The layup is held at 190° C. for seventy minutes. The layup is then allowed to cool 30 minutes to room temperature.
Several 7 inch×8 inch lab scale layups were prepared by the above method using TRL8 and TRL15 resin coated copper sheets (having resin thickness of 8 or 15 microns) manufactured by Circuitfoil and 1000 and 1017 glass cloths. The layups were etched to remove the copper and after etching, the thicknesses of the layups were measured at each corner (upper right hand/upper left hand/lower right hand/ lower left hand) and in the center of the layup. The results are reported in Table 2 below.
These results demonstrate good dimensional stability across the layup.
This application is a divisional of U.S. application Ser. No. 13/404,867 filed on Feb. 24, 2012 which claims priority to provisional application No. 61/446,458 filed on Feb. 24, 2011 the specifications both of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61446458 | Feb 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13404867 | Feb 2012 | US |
| Child | 14196799 | US |
