Stable catalysts for electroless metallization

Abstract

Catalysts include nanoparticles of catalytic metal and cellulose or cellulose derivatives. The catalysts are used in electroless metal plating. The catalysts are free of tin.

Claims

1. A method comprising: a) providing a substrate; b) applying an aqueous catalyst solution to the substrate, the aqueous catalyst solution comprises one or more antioxidants, nanoparticles of metal chosen from silver, gold, platinum, iridium, copper, aluminum, cobalt, nickel and iron, and one or more compounds chosen from polymers having a formula: ##STR00013## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are the same or different and chosen from H, CH.sub.3, CH.sub.2CH.sub.3, CH.sub.2OH, [CH.sub.2CHR.sub.8].sub.xOH, CH.sub.2CH(OH)CH.sub.3, (CH.sub.2CHR.sub.8O).sub.yH, CH.sub.2COOX, C(O)CH.sub.3, C(O)(CH.sub.2).sub.zCH.sub.3 and ##STR00014## wherein R.sub.8 is H or CH.sub.3, n is an integer of at least 2, x, y and z are integers of at least 1 and X is H or a counter cation, and a reaction product of a polymer having a formula: ##STR00015## wherein R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13, R.sub.14, and R.sub.15 are the same or different and are chosen from H, CH.sub.3, CH.sub.2CH.sub.3, CH.sub.2OH, [CH.sub.2CHR.sub.8].sub.xOH, CH.sub.2CH(OH)CH.sub.3, (CH.sub.2CHR.sub.8O).sub.yH, with the proviso that at least one of R.sub.9, R.sub.10, R.sub.11, R.sub.12, R.sub.13, R.sub.14, and R.sub.15 is CH.sub.2OH, [CH.sub.2CHR.sub.8].sub.xOH, CH.sub.2CH(OH)CH.sub.3 or (CH.sub.2CHR.sub.8O).sub.yH, wherein R.sub.8, n, x, y and z are as described above, and a quaternary compound having a formula: ##STR00016## wherein m is an integer from 1 to 16, Y is halogen, Z.sup. is a counter anion, R.sub.16, R.sub.17 and R.sub.18 are the same or different and are H, CH.sub.3 or (CH.sub.2).sub.pCH.sub.3, and R.sub.19 is H or CH.sub.3 and p is an integer of 1 to 9, and one or more cross-linking agents; and the aqueous catalyst solution is free of tin; and c) electrolessly depositing metal onto the substrate using an electroless metal plating bath.

2. The method of claim 1, wherein the substrate comprises a plurality of through-holes.

3. The method of claim 1, wherein the electroless metal plating bath is chosen from a copper, copper alloy, nickel and nickel alloy bath.

4. The method of claim 1, wherein at least one of R.sub.2, R.sub.3, R.sub.5, R.sub.6 and R.sub.7 is CH.sub.2COOX or C(O)CH.sub.3.

5. The method of claim 1, wherein the cross-linking agent is chosen from one or more of haloepoxy compounds and di-epoxy compounds.

6. The method of claim 1, wherein the nanoparticles are 1 nm to 1000 nm.

Description

EXAMPLE 1

(1) Carboxymethyl cellulose/silver catalyst was prepared by dissolving 175 mg carboxymethyl cellulose sodium salt in a beaker containing 500 ml DI water at room temperature. With stirring, 637.5 mg AgNO.sub.3 in 10 ml DI water was added and the mixture was vigorously mixed. 150 mg NaBH.sub.4 in 10 ml DI water was added to the solution mixture with very strong agitation. The solution quickly changed from colorless to reddish brown, indicating reduction of silver ions to silver metal. The solution of the as-synthesized catalyst had a pH between 8 and 9 as measured using an ACCUMET AB15 pH meter. The beaker containing the aqueous catalyst solution was placed in a 50 C. water bath for at least 12 hours to test its stability. After about 12 hours the solution was observed and there was no observable precipitate indicating that the catalyst was still stable.

(2) The catalyst solution was used as a stock solution and 2 aliquots were diluted to nanoparticle concentrations of 300 ppm. The pH of the aliquots was adjusted to 3.5 with ascorbic acid.

(3) Six different laminates were tested: NP-175, 370 HR, TUC-752, SY-1141, SY-1000-2, and FR-408. NP-175 was obtained from Nanya, 370 HR and FR-408 were obtained from Isola, TUC-752 was obtained from Taiwan Union Technology Corporation and SY-1141 and SY-1000 were obtained from Shengyi. The T.sub.g values ranged from 140 C. to 180 C. Each laminate was 5 cm12 cm. A surface of each laminate was treated as follows: 1. Each laminate was immersed into a solvent swell which included ethylene glycol dimethyl ether and water at a volume to volume ratio of 1:2 for 7 minutes at 80 C.; 2. Each laminate was then removed from the solvent swell and rinsed with cold tap water for 4 minutes; 3. Each laminate was then treated with a permanganate aqueous solution which included 1% potassium permanganate at a pH above 10 at 80 C. for 10 minutes; 4. Each laminate was then rinsed for 4 minutes in cold tap water; 5. The laminates were then treated with a neutralizer solution of 3 wt % peroxide and 3 wt % sulfuric acid for 2 minutes at room temperature; 6. Each laminate was then rinsed with cold tap water for 4 minutes; 7. Each laminate was then immersed in an aqueous bath containing 3% CIRCUPOSIT CONDITIONER 231 aqueous acid conditioner for 5 minutes at 40 C.; 8. Each laminate was then rinsed with cold tap water for 4 minutes; 9. MICROETCH 748 solution was then applied to each laminate for 2 minutes at room temperature; 10. Each laminate was then rinsed with cold tap water for 4 minutes; 11. The laminates were then primed for 6 minutes at 40 C. with one of the aliquots of carboxymethyl cellulose/silver catalyst prepared above; 12. The laminates were then rinsed with cold water for 5 minutes; 13. The laminates were then immersed in CIRCUPOSIT 880 electroless copper plating bath at 40 C. and at a pH of 13 and copper was deposited on the substrates for 18 minutes; 14. The copper plated laminates were then rinsed with cold water for 2 minutes; 15. Each copper plated laminate was then placed into a conventional convection oven and dried for 20 minutes at 105 C.; 16. After drying each copper plated laminate was placed in a conventional laboratory dessicator for 20 minutes or until it cooled to room temperature; and 17. Each copper laminate was then tested for adhesion using the conventional Scotch tape test method.

(4) All of the plated copper laminates passed the Scotch tape test. There was no observable copper metal stuck to the Scotch tape after removal of the tape from the copper laminates.

EXAMPLE 2

(5) A 400 ppm aqueous carboxymethyl cellulose/silver catalyst was prepared as described in Example 1. The pH of this catalyst solution was adjusted to pH 3.5 with gallic acid. The six types of laminates described above each with a plurality of through-holes were provided. The through-holes were made conductive by the same process steps and parameters as described in Example 1 for the surface treatment of the laminates. After the catalyst was applied the through-holes were electrolessly plated with the same electroless copper bath described in Example 1.

(6) After plating each board was sectioned laterally to expose the copper plated walls of the through-holes. Multiple lateral sections 1 mm thick were taken from the walls of the sectioned through-holes of each board to determine the through-hole wall coverage for the boards. The European Backlight Grading Scale was used. The 1 mm sections from each board were placed under a conventional optical microscope of 50 magnification. The quality of the copper deposits was determined by the amount of light that was observed under the microscope. If no light was observed the section was completely black and was rated a 5 on the backlight scale indicating complete copper coverage of the through-hole. If light passed through the entire section without any dark areas, this indicated that there was very little to no copper metal deposition on the wall and the section was rated 0. If sections had some dark regions as wells as light regions, they were rated between 0 and 5. The backlight ratings for the 400 ppm carboxymethyl cellulose/silver catalyst on five of the laminates ranged from 4.5 and higher on the 5 scale. The FR-408 laminate had a backlight rating of 4.2. The results indicated that the catalyst is generally acceptable for commercial use by industry standards.