A PROCESS FOR ACCELERATING PD/SN SEEDS FOR ELECTROLESS COPPER PLATING

Abstract: Pd/Sn seeds for electroless copper plating are accelerated by treating them with an alkali metal hydroxide at a pH of about 11.3 and at a temperature above 50°C.

Description: The present invention is concerned with a process for accelerating Pd/Sn seeds for electroless copper plating. The use of Pd/Sn seeds for electroless copper plating is well known. US-A-3,011,920 describes a process to produce seeds which are colloidal particles protected by a coating containing a large amount of tin. The patent describes methods for accelerating such seeds by treatment with a whole range of reagents, including acids, sodium carbonate, sodium pyrophosphate, or sodium hydroxide at a concentration of 5% (see column 5, line 39). The suggested treatment with 5% sodium hydroxide makes no mention at all of temperature In currently used commercial production, acceleration of the Pd/Sn seeds is often accomplished by treatment with hydrochloric acid. According to the present invention, Pd/Sn seeds for use in electro­ less copper plating are accelerated by a process comprising treating them with an aqueous solution of an alkali metal hydroxide at a pH of about 11.3 and at a temperature of above 50°C. Such a treatment selec­ tively removes tin from the surfaces of the seeds while leaving the palladium. This is in sharp contrast to the results obtained using 5% sodium hydroxide as taught by US-A-3,011,920. When the latter process is used, tin still remains a major component of the surface layer of the seeds. The presence of tin on the surface is very undesirable, because it serves to decrease the activity of the seeds, and because it also serves as a source of tin to contaminate the plating bath subsequently used during the electroless deposition of copper. It should be noted that acceleration treatment with hydrochloric acid, as is most commonly done commercially at present, likewise results in seeds still having a large amount of tin on the surface. Pd/Sn seeds typically have a surface having a Pd/Sn ratio of approximately 1 to 5. After acceleration with hydrochloric acid, as is currently used commercially, the Pd/Sn surface ratio is approximately 1 to 2, i.e Sn is still the major component and the 'acceleration' is at best only partially effective. By the process of the present invention, however, there are obtained treated seeds having a Pd/Sn ratio of 5 to 1. Electroless copper plating is a process of very great importance in, for example, the manufacture of circuit boards. Typically, circuit boards are made of resin, i.e an epoxy resin. The process of the present invention is particularly advantageous when used for the treat­ ment of seeds on such a substrate. It must be emphasised that the alkali metal hydroxide solutions used in the present invention have a pH about 11.3 i.e. they are quite weakly basic. Sodium hydroxide is the preferred alkali metal hydroxide and it is present at a concentration of approximately 0.005%, i.e a concentration only one part in a thousandth of that mentioned in US-A-­ 3.011,920. In the process of the present invention, it is essential that the seeds are treated at a temperature above 50°C. The preferred tempera­ ture is about 73°C. This is in sharp contrast to US-A-3,011,920 which does not specify any temperature for the treatment.

Claims: 1. A process for accelerating Pd/Sn seeds for electroless copper plating, the process comprising treating the seeds with an aqueous solution of alkali metal hydr­ oxide at a pH of about 11.3 and at a temperature of above 50°C, thereby reducing the proportion of Sn in the surface layer of the seeds. 2. A process as claimed in claim 1, wherein the aqueous metal alkali hydroxide is sodium hydroxide. 3. A process as claimed in claim 2, wherein the sodium hydroxide is in a concentration of about 0.005%. 4. A process as claimed in any preceding claim, which is performed at a temperature of 73°C. 5. A process as claimed in any preceding claim, which is performed on Pd/Sn seeds disposed on an epoxy resin substrate.

Inventors: ALNOT, PATRICK RENE, AUERBACH, DANIEL JONATHAN, BRUNDLE, CHRISTOPHER RICHARD, MILLER, DOLORES CARLOTTA
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1986
Main classification: C23C18
IPC codes: C23C18