EP0882108A1

EP0882108A1 - Polyamide based laminating, coverlay, and bond ply adhesive with heat activated cure component

Info

Publication number: EP0882108A1
Application number: EP97907743A
Authority: EP
Inventors: Thomas F. Gardeski
Original assignee: ICI Americas Inc
Current assignee: Zeneca Inc
Priority date: 1996-02-23
Filing date: 1997-02-21
Publication date: 1998-12-09
Also published as: WO1997031078A1; AU1966297A; JP2001513115A; KR19990087191A

Abstract

A high performance laminating, coverlay, and bond ply adhesive which includes a high molecular weight acid terminated thermoplastic polyamide resin, an epoxy, and a high molecular weight polyester component which can be heat cured with silane and aziridine curatives to form an extremely high temperature resistant, flexible, and high bond strength adhesive is disclosed. The adhesive can be used to enhance the characteristics of polyester and polyethylene naphthalate films for use in flexible and rigid board circuitry applications as well as being an excellent adhesive for films such as polyimide for the same applications thus allowing the films to be used at temperature which are capable of withstanding high temperatures. Along with being useful as laminating adhesive, the system is stable at room temperature and thus can be stored as a free film bond ply adhesive or coated on a film for future conversion into laminate or coverlaying of electronic circuitry.

Description

POLYAMIDE BASED LAMINATING. COVERLAY. AND

BOND PLY ADHESIVE WITH HEAT ACTIVATED

CURE COMPONENT

BACKGROUND OF THE INVENTION

This application is based on U.S. provisional patent application 60/012,164, filed on February 23, 1996.

The growth of electronic circuitry has been dramatic due to the onset of portable computers, lap top computers, portable cellular phones, calculators, smart cards, and the like. However, cost constraints have been a limiting factor. Polyimide films, long a staple in the electronics industry, were required to meet the performance standards set by the U.S. Military. However, when used for commercial applications, their cost is proving to be prohibitive for many applications. With the onset of new films, such as polyethylene naphthalate, new adhesive systems which can achieve the highest performance possible are required. Most adhesives used for polyimide films, such as acrylic, require processing temperatures that are detrimental to the film and also lack the adhesive affinity required for most circuitry applications. A compatible adhesive with processing parameters which are not detrimental to the film, while providing the necessary heat resistance, chemical resistance, and environmental stability, is required.

As important as the need for the aforementioned adhesive, a second need exists for an economical, moderate temperature-processing adhesive which can advantageously provide the thermal potential required of polyimide films. Currently, in order to achieve circuitry which can be functional at the high temperature capabilities of polyimide film, adhesives which process at temperatures of greater than 275° C are required. Most circuit manufacturers can not achieve these temperatures with their equipment, and these extreme temperatures also have adverse effect on a conductive substrate, such as copper, mandating that a vacuum be used in the processing to remove air which causes oxidation ofthe conductive substrate.

Another area requiring an improved adhesive is in the field of flat circuitry. As circuitry becomes finer, with lines and spaces approaching 1 mil in thickness, the need for flat, dimensionally stable circuitry materials is required. Current adhesives, when cured to the levels required to achieve the desired thermal stability characteristics and chemical resistance, tend to shrink after processing, thus leading to a curled laminate which is difficult to image and subsequently etch. This creates a continued need in the art for an adhesive which will have the required thermal stability, while behaving like a thermoplastic and not "draw back" after cure.

There, therefore, continues to remain an urgent and unfulfilled need in the art for an adhesive which can advantageously address and resolve these problems. Summary of the Invention

As discussed hereinafter, the present invention surprisingly and unexpectedly provides an adhesive which addresses the above-described problems and shortcomings in the art. In accord with the present invention, it is thus an object ofthe present invention to provide an improved and novel high performance laminating, coverlay, and bond ply adhesive having excellent encapsulating and dimensional stability properties.

It is a further feature ofthe present invention to provide an improved adhesive for the bonding of electronic circuitry materials.

It is another feature ofthe present invention to provide an adhesive with a three stage cure sequence which links high molecular weight components to provide for highly cross-linked components in a block copolymer fashion. It is yet another feature ofthe present invention to provide an adhesive, which when cured, allows for flat base circuity materials.

It is still a further feature, also unique to this invention, to allow for the incorporation of lower temperature films, such as polyethylene naphthalate or polyethylene terephthalate, which can be used as lower cost alternatives to polyimide films in commercial electronic circuitry applications. It is still yet a further aspect ofthe present invention to provide for an adhesive system that can withstand the operating temperature limits of polyimide films, e.g., can be processed at up to 650°F. These and other objects are accomplished by way ofthe present invention which advantageously provides an adhesive which is the reaction product of polyamide and polyamide/aziridine/polyester linkages with an epoxy and silane.

The foregoing and other features ofthe present invention are accomplished by an adhesive which is a reaction product as described hereinafter. The initial reaction provides for linking the acid terminating groups of a high molecular weight thermoplastic polyamide to those of a high molecular weight thermoplastic polyester with an aziridine component to provide for amide linkage sites between the two components in addition to those already present in the polyamide. A second reaction is carried out by reacting the polyamide/aziridine/polyester sites and the already incoφorated polyamide sites ofthe polyamide component with an epoxy, such as bis epi epoxy, thus forming a block copolymer of long segments of polyamide polyester/polyamide in which the polyamide and polyamide/polyester sites are reacted with epoxy in a parallel fashion. A third reaction carried out is that of a glycidoxyalkoxysilane, which is incoφorated as a bond enhancer, with the amide and formed polyamide aziridine/polyester linkages to provide for the adhesive ofthe present invention. The first reaction is accomplished at room temperature, while the second and third steps are carried out at temperatures of 300° to 350°F to achieve full cure. Prior to the final heat cure, a cast or coated film, to which the adhesive ofthe present invention has been applied, can be stored at room temperature while awaiting processing into the final desired laminate or coverlay configuration.

Accordingly, another aspect ofthe present invention is directed to a process of making the adhesive ofthe present invention which comprises linking a high molecular weight acid terminated thermoplastic polyamide resin with a high molecular weight polyester resin via an aziridine which forms polyamide and polyamide/aziridine/polyester linkages, then reacting with an epoxy and a silane via the amide groups in the polyamide and the formed polyamide/aziridine/polyester linkage.

A further aspect ofthe present invention is an article having at least two surfaces bonded together by applying to said surfaces the adhesive ofthe present invention. Accordingly, the invention also encompasses composite or laminate articles having surfaces bonded together by the present adhesive.

The adhesive ofthe present invention advantageously possesses excellent encapsulating properties with regard to circuit conductors while also unexpectedly providing virtually unmeasurable flow onto metal pads. Flow of adhesives onto pads requires manual cleaning with solvents which is very time consuming. The present adhesive advantageously avoids this costly step and thus advantageously speeds up the process of flexible circuit manufacturing. The adhesive ofthe present invention is thus suφrisingly vastly superior to any other adhesive currently available for use in circuitry processing. An extremely high temperature resistant, flexible, and high bond strength adhesive is suφrisingly provided by way ofthe present invention. The adhesive can be advantageously used to enhance the properties of polyester films such as polyethylene terephthalate and polyethylene naphthalate films for use in flexible and rigid board circuitry applications. The present invention also provides an excellent adhesive for films such as polyimide for the same applications. This allows the films to be used at temperatures which are capable of withstanding high temperatures, which to date has been limited by currently available adhesives. Along with being useful as a laminating adhesive, the adhesive is stable at room temperature and thus can be advantageously stored as a free film bond ply adhesive or coated on a film for future conversion into a laminate or coverlaying of electronic circuitry. These and other features, aspects, and advantages ofthe present invention will become better understood with reference to the following description and appended claims.

Detailed Description of the Invention The present invention provides an adhesive having excellent encapsulating and dimensional stability properties, which adhesive comprises a reaction product of a block copolymer of polyamide and polyamide/aziridine/polyester linkages with an epoxy and a silane. Dimensional Stability denotes the amount of shrinkage in the Machine and Transverse Direction of a film or substrate after being exposed to a given temperature for a given period of time, e.g., measurement ofthe film in both directions before and after exposure to 150°C for 30 minutes with log results in % change.

A process of making the adhesive ofthe present invention comprises linking a high molecular weight polyamide component with a high molecular weight polyester component via aziridine as follows: H H

R, = High Molecular Weight Polyamide

X = Aziridine Repeating Unit

R, = High Molecular Weight Polyester

A second step comprises reacting the polyamide linkage and the formed polyamide/aziridine/polyester linkage with an epoxy as follows:

wherein y represents epoxy, e g , bis epoxy The third step for the process of making the present adhesive comprises reacting a silane, such as a glycidoxyalkoxysilane, e.g., glycidoxypropyltrimethoxysilane, with the high molecular weight polyamide and the formed linkage between the high molecular weight polyamide and the high molecular weight polyester by result ofthe aziridine reaction. This can be illustrated as follows:

N - H + OCH_jCHCH, - O - (C¥L)3 - Si - (OCH₃)₃

I 250° to 400°F

N I HCH

HCOH

I

O

I HCH

HCH HCH

I Si

I

HO CH, HO CH, HO CH, Reacting one end ofthe glycidoxypropyltrimethoxysilane with the polyamide and formed aziridine linkage between the polyamide and polyester links the glycidoxypropyltrimethoxysilane with the block copolymer structure, while also allowing for a "free end" to provide for wetting ofthe surface of the film/foil to advantageously provide for more intimate contact between the block copolymer structure with the surfaces to be bonded The resulting reaction product is the adhesive copolymer ofthe present invention having the formula:

Minor Repeating Unit wherein the minor repeating unit constitutes from about 1% to about 5% ofthe total weight ofthe copolymer and the major repeating unit constitutes from about 95 to about 99% ofthe weight ofthe adhesive copolymer. R, R^ X and Y are also defined as described previously.

The presence of greater than 5% of the minor repeating unit in the copolymer can result in undesirable plasticizing effects.

Suitable constituents for use in the present invention are described hereinafter.

By high molecular weight polyamide is meant a polyamide having a molecular weight of at least 5,000; particularly from about 5,000 to about 100,000; and more particularly from about 20,000 to about 50,000.

By high molecular weight polyester is meant a polyester having a molecular weight of at least 10,000; particularly from about 10,000 to about 200,000; and more particularly from about 20,000 to about 50,000.

Examples of suitable polyester, epoxy and aziridine components for practice in the present invention are disclosed in United States Patent

Numbers 5,095,077 and 5,194,307, which are incoφorated herein by reference.

With regard to the epoxy component, U.S. Patent Nos. 5,095,077 and 5, 194,307 describe the requirement of an electronic grade of epoxy. Such grade of epoxy, while suitable if desired, is advantageously not required to carry out the present invention. Thus, for example, a bis-epi epoxy is suitable in the practice ofthe present invention.

Examples of non-limiting types of silanes include glycidoxyalkoxysilanes such as glycidoxypropylmethyldiethoxysilane and glycidoxypropyldimethylethoxysilane.

Heptafluoroisopropoxyproplymethylcidhlorosilane is also suitable.

Glycidoxypropyltrimethoxysilane is especially preferred.

Non-limiting examples of suitable types of polyamides include: Versamid 744 Softening point of 125°C, Versamid 744 Softening point of

125°C, Versamid 756 Softening point of 110°C,

Versamid 757 Softening point of 115°C, and Versamid 759 Softening point of 110°C. Versamid 972 Softening point of 130°C is particularly preferred. The novel adhesive ofthe present invention preferably comprises a reaction product of an acid terminated thermoplastic polyamide component such as that sold by Henkel under the name of Versamid 972, a polyester/epoxy composition containing a glycidoxypropyltrimethoxysilane sold by Morton under the trade name of Adcote 76PI, and an aziridine component, such as that sold by EIT, Inc. under the trade name of XAMA 7. The adhesive ofthe present invention provides a fully crosslinked network without the evolution of volatile by-products to provide an advanced laminating, coverlay, and bond ply adhesive for film to film, foil to film, foil to foil, and hardboard to hardboard applications. The adhesive has excellent flexibility, superior bond strength, solder resistance, moisture and chemical resistance and superior Z-axis stability along with continuous and/or deferred processing capability. The adhesive can be stored for long periods of time, e.g., up to one year, prior to the implementation ofthe above-described curing process. The adhesive can be coated on an insulating film or release substrate by a continuous process and stored at room temperature indefinitely prior to further processing, or laminated in-line to various foils or films. The adhesive ofthe present invention can be advantageously cured without the evolution of volatile by-products to provide a flexible bond-ply with superior overall properties to any currently available system with the added advantage of excellent Z-axis stability.

The following examples are provided to illustrate the present invention and should not be construed in any manner whatsoever as limiting the invention. EXAMPLE 1

A mixture was prepared from the following components: A high molecular weight acid terminated thermoplastic polyamide resin at 20% solids in n-Propanol sold by Henkel under the trade name of Versamid 972, a mixture of high molecular weight polyester with residual acid functionality, bis-epi flexible epoxy, and glycidoxypropyltrimethoxysilane at 51% solids in methyl ethyl ketone sold by Morton under the trade name of Adcote 76P1 and a polyfunctional aziridine sold by EIT. Inc. under the trade name of XAMA 7. The mixture was then made by combining 88 parts by solids ofthe polyester/epoxy component to 9 parts by solids ofthe polyamide component.

The mixture was then allowed to stand for 30 minutes at room temperature to assure a homogeneous solution. To this mixture was added 3 parts by solids ofthe aziridine component. The mixture was then allowed to stand for 30 minutes to allow for the onset ofthe aziridine reaction with both the acid groups of the polyamide and polyester components. The mixture was then bar coated to yield a one mil dry coat onto a sheet of 5 mil thick polyethylene-naphthalate film sold under the trade name of KALADEX by ICI Films, then dried for 10 minutes at 225°F to remove the solvents and allow for the onset ofthe epoxy and glycidoxypropyltrimethoxysilane reaction with the polyamide linkage and the formed linkage between the polyamide and polyester components by the aziridine component. The adhesive coated film was then placed over a sheet of 1 oz rolled annealed copper, placed between two 2 mil thick skived TFE press pads, then placed between two one-quarter inch thick stainless steel caul plates. The entire lay-up was then placed in a press at room temperature under 50 psi of pressure. The press was then heated to 350° F over a period of 14 minutes, allowed to remain at 350°F for 1 hour, then cooled to 200°F by running air through the press platens followed by water to cool the press to 150°F at which point the lay-up was removed. The subsequently formed laminate of polyethylenenaphthalate film/adhesive/copper was removed and allowed to condition at room temperature for 24 hours. The formed laminate was then tested in accordance with IPC-FC-241 procedures to yield the following properties: Initial Peel δ to lO PLI

Peel after 5 second exposure to 500°F solder 8 to 10 PLI

Solder float at 500°F Pass*

Solder float at 550°F Pass*

Solder float at 600°F Pass* Solder float at 650°F Pass*

*Film began to melt but no blistering or delamination was present.

EXAMPLE 2 The mixture from Example 1 was coated onto 2 mil thick polyimide film sold by UBE Industries of Japan under the trade name of UPILEX S, then dried and pressed under the same process as described in Example 1.

The resulting laminate exhibited a bond strength of 10 PLI both before and after exposure to 650°F solder for 10 seconds. After a two minute exposure to solder at 650°F, no blistering, delamination, or any other detrimental effects were observed. EXAMPLE 3

A mixture of 93.1 parts by weight of Morton 76 Pl is combined with 4.7 parts by weight of Versamid 972. After standing for 30 minutes, 2.2 parts by weight of XAMA 7 was added, then the mixture was allowed to sit at room temperature for 30 minutes. The following smart card laminate construction was then prepared in the same fashion as that of Example 1 :

5 mil polyethylenenaphthalate film/ adhesive/ 1 oz. rolled annealed copper/adhesive/5 mil polyethylene naphthalate film/adhesive/5 mil polyethylene naphthalate film/adhesive/5 mil polyethylenenaphthalate film. Upon removal from the press, no lift could be measured on any corner ofthe film. The same construction made from the adhesive described in U.S. Patent No. 5,095,077 exhibited lift of 9 to 10 mm in each corner ofthe constructions, beyond the 5mm allowance specified by the smart card manufacturer.

EXAMPLE 4 A mixture was prepared consisting of 88 parts by solids of Morton 76 Pl and 9 parts by solids of Versamid 972 and allowed to stand at room temperature for 30 minutes. Three parts by solids of XAMA 7 was then added to the mixture and allowed to sit at room temperature for 30 minutes.

This mixture was then coated onto a sheet of 50 micron thick KALADEX 2000 and dried at 225° F to yield a dry coating of 25 microns in thickness. The resulting coated sheet was then laminated to loz. ED copper foil incoφorating the same parameters of Example 1. The resulting laminate was allowed to stand at room temperature for 12 hours and then processed into

Flexible Printed Circuitry using the following procedures.

Drilling and Routing

Both the KALADEX and adhesive drilled and routed excellently by way of a score. No debris was generated nor did any residual film/adhesive remain on the equipment or material.

Riston Lamination: Processed normally when the Riston (photo-resist) was laminated to the copper side ofthe laminate at 140° to 145°F. Photo-exposure: Processed normally Development: Processed normally Etching: The resulting circuit pattern was etched with cupric chloride at 130° to 135°F. Both the KALADEX and adhesive showed no attack in exposure to this etching process.

Coverlay The formed circuitry pattern was then coverlayed with a sheet of 50 micron KALADEX coated with the same mix of adhesive at 25 micron dry thickness in a press under 100 psi for 1 hour at 350°F. The coverlayed circuit was then critically examined under 100X magnification to determine how well the adhesive encapsulated the etched circuit conductors and to determine the amount of flow of adhesive onto exposed copper pads used for solder interconnects. The encapsulation was deemed exceptional and the flow onto the pads virtually unmeasurable, which was vastly superior to any other adhesive system used in circuitry processing currently available.

Hot Oil Leveling The coverlayed circuitry was then exposed to hot oil leveling by submersion in hot oil for 20 seconds at 460°F. Upon removal from the hot oil, the circuitry was examined and determined to process as well as polyimide-based circuitry constructions from the criteria of lay-flat characteristics and other critical parameters.

Punching

The circuitry was then punched from the laminate. Dimensional stability was deemed as excellent, as the pre-drilled registration holes fit very nicely onto the pins on the fixture used to hold the circuit in place during the punching process. In addition, the film and adhesive punched very cleanly, leaving no debris on the tool or in the punched holes.

Hand Soldering The circuitry was hand soldered using a solder iron with a tip temperature of 650°F with a Tin/Lead based solder composition. Neither the hot solder or direct contact with the solder iron tip had any adverse effect on the adhesive system.

While this invention has been described in terms of various embodiments, one of skill in the art will readily appreciate that various modifications, substitutions and changes may be made without the exercise of undue experimentation and without departing from the spirit thereof. Accordingly, it is intended that the scope ofthe present invention be limited solely by the scope ofthe following claims, including equivalents thereof.

Claims

1. A process of making an adhesive which comprises linking a high molecular weight acid terminated thermoplastic polyamide resin with a high molecular weight polyester resin via an aziridine, which forms polyamide and polyamide/aziridine polyester linkages, then reacting with an epoxy and a silane via the amide groups in the polyamide and the formed polyamide/aziridine/polyester linkages.

2. The process of claim 1 comprising 5% to 95% by weight of said polyester and 95% to 5% of said polyamide.

3. The process of claim 1 wherein the polyester group has an acid functionality as determined by an acid number of 0.05 to 0.19.

4. A laminate made with the adhesive made by the process of claim 1 which comprises polyethylenenaphthalate film and copper, said laminate being capable of withstanding solder temperatures of 550°F.

5. A laminate made with the adhesive made by the process of claim 1 which comprises polyimide film and copper, said laminate being capable of withstanding solder float temperature of 650°F for at least about 2 minutes without any deterioration ofthe laminate.

6. A multiple laminate made with the adhesive made by the process of claim 1 which exhibits less than a 5mm lift in any corner ofthe construction. An adhesive which comprises a block copolymer ofthe formula:

wherein R, is a high molecular weight polyamide; wherein R, is a high molecular weight polyester; wherein X is an aziridine repeating unit and wherein Y is an epoxy.

8. The adhesive of claim 7 wherein the minor repeating unit constitutes from about 1% to about 5% ofthe total weight ofthe copolymer and the major repeating unit constitutes from about 95 to about 99% ofthe total weight ofthe copolymer.

9. The adhesive of claim 7 wherein the polyester is of an acid functionality as determined by an acid number of 0.05 to 0.19.

10. The adhesive of claim 9 wherein the polyester has a melt temperature of at least about 125°C.

11. A composite comprising a first construction material, a second construction material, and an adhesive between a first surface ofthe first construction material and a first surface ofthe second construction material, the adhesive comprising a block copolymer ofthe formula as in Claim 7.

12. The composite of claim 11 wherein the first and second construction materials are selected from the group consisting of a polyester, a polyimide, polyethylene naphthalate, a metal foil and a hardboard.

13. A process of making an adhesive, which adhesive comprises a block copolymer ofthe formula as in Claim 7 and which process comprises the steps of: a) reacting a polyamide and a polyester with an aziridine, so that a copolymer of polyamide and polyester, linked by aziridine, is formed, and b) reacting the copolymer of a) with an epoxy and a glycidoxyalkoxysilane.

14. The process of claim 13 wherein the glycidoxyalkoxysilane is glycidoxypropyltrimethoxysilane.

15. The process of claim 14 wherein the epoxy is bis-epi epoxy.

16. A process of making a composite structure or a storage medium which comprises the steps of: a) reacting a polyamide and a polyester with an aziridine, so that a copolymer of polyamide and polyester, linked by aziridine, is formed; b) mixing the copolymer with an epoxy and a glycidoxyalkoxysilane; and c) applying the mixture to a surface of a substrate requiring an adhesive, prior to heat curing the copolymer, the epoxy and glycidoxyalkoxysilane.

17. The process of claim 16 wherein the copolymer is heat reacted with the epoxy and glycidoxyalkoxysilane.

18. The process of claim 17 wherein the heat reaction is carried out at a temperature ranging from about 250°F to about 400°F.

19. The process of claim 16 wherein the polyamide, the polyester, the aziridine, the epoxy, and the glycidoxyalkoxysilane are mixed together prior to the reacting step a).

20. The process of claim 16 wherein the substrate is selected from the group consisting of a film substrate, a foil substrate, and a hardboard substrate.

21. An article having at least two surfaces bonded together by applying to said surfaces the mixture of c) of claim 16 and causing a reaction between the copolymer and the epoxy and glycidoxyalkoxysilane.

22. A composite article of a film to film bonding, foil to foil bonding, or foil to film bonding having surfaces bonded together by applying to said surfaces the mixture of c) of claim 16 and causing a reaction between the copolymer and the epoxy and glycidoxyalkoxysilane.

23. A copolymer ofthe formula:

R, O fC (CONH) N-X-N (CH-),C IOR,

wherein R, is a high molecular weight polyamide; wherein R, is a high molecular weight polyester; and wherein X is an aziridine repeating unit.

24. A process of using the copolymer of claim 23 to make an adhesive block copolymer which comprises reacting the copolymer of claim 23 with an epoxy and a glycidoxyalkoxysilane.

25. A process of making the copolymer of claim 23 which comprises reacting a polyamide and a polyester with an aziridine.

26. A block copolymer ofthe formula:

wherein R, is a high molecular weight polyamide; wherein R, is a high molecular weight polyester; wherein X is an aziridine repeating unit; and wherein Y is an epoxy.

27. An adhesive having excellent encapsulating and dimensional stability properties which comprises a reaction product of polyamide and polyamide/aziridine/polyester linkages with an epoxy and a silane.

28. The adhesive of claim 27 wherein the silane is a glycidoxyalkoxysilane.

29. The adhesive of claim 28 wherein the glycidoxyalkoxysilane is glycidoxypropyltrimethoxysilane.

30. The adhesive of claim 27 wherein the epoxy is bis-epi epoxy.

31. A polyester or polyimide film coated with the adhesive made by the process of claim 1, which coated film can be stored at room temperature for up to one year, and processed into metal clad laminate or as a coverlay construction for printed wiring boards.

32. The film of claim 31 wherein the polyester is selected from the group consisting of polyethylene naphthalate and polyethylene terephthalate.