IL43636A - Plastic-metal laminate and a method for its manufacture - Google Patents

Description

Plastic metal laminate and method for its manufacture MacDermid Incorporated 41785 Abstract of the Disclosure An improvement is obtained in the bond strength between members of a laminate comprising a plastic substrate and a metal film through a process of first laminating to the plastic substrate a anodized metal foil by heat and chemically stripping the foil from the substrate activating the surface for electroless plating and electrolessly depositing a metal wherein the substrate is contacted with an aqueous solution containing an organic silicon compound at some stage subsequent to said chemical stripping The final metal film when applied to the substrate exhibits consistently better adhesive strength than is obtained without the organic silicon Background of the Invention This invention relates to a method of preparing a plastic substrate to improve the characteristics of its surface for the bonding thereto of a subsequently applied metal such as an electrolessly deposited metal The invention relates both to an improved laminate comprising a plastic substrate and metal as well as to the substrate useful especially in the production of circuit boards for electrical and electronic The method here disclosed is generally similar to that disclosed in Patent and is a modification of the procedure disclosed in Israel The la procedure involves l foil by to of which ia ultimately to or foil is or surfaces which ia known Application ssacrificial stripping of plastic a topography on the that characteristics for This ia to the in foregoing by the of plantic substrate to contact a solution containing an at o to of the sacrificial foil the obtained by this only in bonding or peel substrate bat especially in of after of e to for of wain of printed in additive circuits in is that they ibit of the final coating to plastic has a of ap linear for adhesion the metal and plastic with ia the requirement a satisfactory printed circuit tna bond be stable at temperatures up to around S to printed boards as today subject to soldering operations of this which operations are to permanently mount the various electronic components of electrical circuit on the Quito such soldering operation partially and momentarily holding board in a bath of solder in order to affect soldering of all junctions in one This produces substantial shock to the It is that such soldering operation not weaken olymer bond below the industry as to bond It found during extensive that many occasions arise where printed circuit boards show adhesion at roots but that dramatic decrease or results because of soldering or other high temperature It accordingly objective of the present invention to provide a metho of producing consistently higher peel strengths between metal conductor film and its supporting plastic to able to do this over a wider range of operating conditions in the preparation of a printed and thus greater tolerance for variables which inherently unavoidably arise in the commercial production operations It is especially an objective of this invention to materially improve resistance of the final noted briefly above it has not been found that contacting the surface of the plastic at some subsequent the step of chemically stripping the sacrificial with a of silicon derivative especially of the comprising the amino substituted results in substantially improving the adhesion of the conductor to the substrate both before soldering The can applied fror either aqueous or solution and constitute a totally step the process of effecting an depos on the or it raay be incorporated in one of the activating plating operations The by which the silicon derivative exerts its favorable reaction is not well However it that the effect is one of slowing down the rate of deposition of the electroless whereby there is opportunity for the metal to fill the laicroscopie reproduced in the surface of the substrate by the sacrificial It is postulated that the slowing of of deposition of electroless helps to prevent the of the crevices by the before a root or anchor is established in the interstices by the depositing in electroless deposition Whatever the the presence of trace amounts of silicon on the surface during the deposition provides a definite Silicon and silanes in been widely used in industry to promote the properties of various Filled are made blending into the during its operation particles of sand and other Silanes have been used to promote the wetting of solid particles with the polymers during the molding thereby avoiding or separation of the plastic from the filler during mechanical There are numerous references in the literature relating to the use of silicon derivatives or reactive silanes in various interfacial One excellent reference is entitled Silanes as Adhesion Promoters to Hydrophillic by Edmond published by Dow Corning in the aforementioned Israel Patent Specification the use of silanes during interfacial contacting of the sacrificial metal foil and plastic substrate is It has also been proposed in the prior patenr as for example in Patent and to incorporate silicon compounds directly in the electroless plating So far as it is there has been no previous suggestion for using silane materials in combination with the sacrificial metal foil where the silane is brought into contact with the substrate surface at any stage subsequent to the chemical stripping of the sacrificial This procedure appears to afford certain advantages and improvements when used in place or in conjunction the silane treatment taught in the aforesaid Israel Patent Specification or in the prior A wide variety of organic silicon derivatives is available but apparently not all are useful in the practice of the invention herein The best results are obtained by the use of and more particularly there is preferred for commercial practice of invention a rather c type of having the general wherein a lower to amino substituted and is a lower to 3 Tho following illustrate the invention but it is understood that are not to be considered as comprehensive of all silicon derivatives useful in the of the A foil is firet prepared by β to that described in patent Example This comprises taking a of foil of approximately 2 thickness it in an alkaline soak cleaner bath for 5 at a of around to surface and Tho clean foil is etched slightly in solution at room for 3 to anodic treatmen in an electrolytic bath containing phosphoric acid by at for about 3 minutes at a current of The foil dried for about 2 at and to a plastic Tho substrate consists of plies 8 i of glass fiber reinforced exarsple Precision and the composite of renin and foil is placed in a lasiinating using a as a atrip of between the foil and platen in order to prevent sticking during The larainating press is preheate to a of around is closed and components at a of for 30 seconds after which pressure is raised 250 the curing is at ature and pressure for about 60 The a resin substrate having the to its This clad is optionally cleaned of any surface sprayed or otherwise contacted with an solution capable of dissolving away all visible traces of the As described in VII of the aforesaid patent any of the usually aluminum etchant such as hydrochloric acid by or alkali hydroxide by is Typical conditions a solution of to about preferably for a period of 2 to 30 but normally about 5 at the preferred When the substrate is free of it is in phosphoric bath containing by of phosphoric for about 7 at after which it is thoroughly The next placed in an aqueous solution of propyl in leopropanol for 3 minutes at room of the is 4 in this The is rinsed and is then ready for activation In this the is the activation technique described in patent This comprises the substrate in hydrosol activator in accordance with the teaching of the for 3 at carefully then the in accelerating solution of rinsing again and placing substrate a plating solution etex for a period of about 20 Minutes at r finally and electroplating additional copper deposit to a thickness of about 1 The plated substrate is and then to an oven bake at 30 for about 1 The adhesion of the plated deposit the plastic substrate of this was checked by standard technique of the pull of a w strip of peeled the su and pulled at to that The average adhesion value was found to be to 10 of the plated was for 10 on the sur of a solder pot filled with solder at temperature of the adhesion test a value of to 10 per purposes of a plated board is prepared using identically procedure described above except that the of the substrate in the bath is The adhesion of this is found to be about 4 to C pounds per inch before thermal and 3 to 4 pounds after such II The foregoing procedure was duplicated except in this instance the plastic substrate in the solution was done after the activating ste rather than before All other conditions the in this case values for deposited copper 9 to 10 pounds the of I followed with the that instead of the substrate to contact with the in silane in the copper of the in that solution was at 4 as In this the peel strength of the resulting plated substrate to on the order 9 pounds before solder and 10 pounds 10 second shock in solder at 5 IV The X repeated the exception th instead of a separate of in a the incorporated the fluoro acid accelerator solution In this about 10 of the and the substrate in solution for about 4 of lating operations are The this procedure is about 10 pounds per inch a 10 second shock dip in solder at v The of 1 is repeated the of the la in the silane solution after the sacrificial foil Instead of then a the laminates is subjected to a conventional vacuum metallizing Exeellent adhesion is obtained between the metal and Example VI procedure of any of the foregoing examples is the same except that instead of copper plating the it is electrolessly nickel Any commercial electroless nickel may be such as produces by Alternatively a commercial electroless cobalt deposit may be In each the adhesion is consistently improved over laminates not subjected to the silane It appears that the same silane compositions disclosed in the aforesaid Patent Specification 43087 are particularly useful in the practice of this These silane propyltrimethoxy silane C C trimethoxy silane trimethoxy silane silane In all an optimum concentration of the silane mixture of appears to be about 4 ml per liter of However some improveaient in adhesion is evident as of while generally no is at levels about The prefera in aqueous solution since this is principally in conventional plating solvents for can be substitute especially separate step is as in I II insufficientOCRQuality

Claims (18)

1. The metho'd of improving the adhesion between a molded plastic substrate and a deposited film of metal formed in situ on the substrate by electroless metal plating or vacuum metallizing processes, which comprises the steps of first forming a laminate of the plastic substrate and a sacrifidal metal foil by bonding said foil to said substrate with heat and pressure, chemically stripping said sacrificial foil from the laminate thus formed, contacting said stripped substrate at room temperature with a dilute solution of an organic silicon compound preliminary to in situ deposition of the metal film thereon, wherein said silicon compound is present in solution from about 0.5 ml/1 to 5.0 ml/l, said substrate being maintained in contact with said organic silicon solution for a period of from thirty seconds to five minutes.

2. The method as defined in 'Claim 1 , which includes the steps of activating said stripped substrate for electroless deposition and electrolessly depositing said film of metal thereon after contacting said substrate with said dilute organic silicon compound solution.

3. The method as defined in Claim 1, wherein said substrate is contacted with said organic silicon compound in solutioji after stripping said sacrificial foil and prior to activation of said substrate.

4. The method as defined in Claim 2, wherein said substrate is contacted with said organic silicon compound in solution 'after activation of said substrate surface and prior to electroless deposition of metal thereon. 43636/2

5. The method as defined in Claim 2, wherein said substrate is contacted with said organic silicon compound in solution with sasfcd metal to be electolessly deposited.

6. The method as defined in Claim 2, wherein said organic silicon compound is a silane.

7. The method as defined in Claim 6, wherein the plastic substrate is formed of an epoxy resin.

8. The method as defined in Claim 2, wherei the plastic substrate is formed of an epoxy resin.

9. The method as defined in Claim 6, wherein said silane has the general formula: R*Si (R1)3 where R is an amino substituted lower alk l radical and is a lower alkanoxy radical.

10. The method as defined in Claim 9, wherein said sacrificial metal foil is aluminum anodized in phosphoric or sulfuric acid solution.

11. The method as defined in Claim 9, wherein said plastic substrate is formed of an epoxy resin.

12. The method as defined in Claim 9, wherein said silane is a member of the group consisting of amino propyl trimethoxy silane and amino ethyl amino propyl trimethoxy silane.

13. The method as defined in Claim 9, wherein said silane is in aqueous solution and contains from about 0.5 ml to 5 ml per liter of said silane.

14.The method as defined in Claim 13, wherein said substrate is immersed in said silane solution for from 30 seconds to 5 minutes at room temperature.

15. The method as defined in Claim lf wherein the metal film is applied by vacuum metal deposition. 43636/22

16. A laminate comprising a plastic substrate and an eleetrolessly deposited metal film adhered thereto to provide a peel strength of at least about 8 pounds per inch after exposure to a temperature of the order of 500°F, wherein said substrate has been contacted by a solution containing an organic silicon compound as defined in Claim 1.

17. A laminate comprising a plastic substrate and an eleetrolessly deposited metal film adhered thereto to provide a peel strength of at least about 8 pounds per inch after exposure to a temperature of the order of 500*F, wherein said substrate has been contacted by a solution, of a silane as defined in Claim 9».

18. A laminate as defined in Claim 17, wherein said eleetrolessly deposited metal is a member of the group consisting of copper, nickol and cobalt. ND/AJ