Browse Prior Art Database

Lead Control in Electroless Nickel-Boron Bath

IP.com Disclosure Number: IPCOM000036095D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Schmeckenbecher, AF: AUTHOR [+2]

Abstract

A method has been developed for controlling the Pb ion concentration in the Ni-B plating solution used for plating molybdenum lands on multi layer ceramic (MLC) substrates in semiconductor devices. The proposal involves the introduction of Pb molybdate to the bath which ionizes and acts as a buffering agent.

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Lead Control in Electroless Nickel-Boron Bath

A method has been developed for controlling the Pb ion concentration in the Ni-B plating solution used for plating molybdenum lands on multi layer ceramic (MLC) substrates in semiconductor devices. The proposal involves the introduction of Pb molybdate to the bath which ionizes and acts as a buffering agent.

Electroless plating solutions [*] are used to plate a nickel layer on the Mo lands. The plating bath is stabilized so as not to plate Ni on the unactivated ceramic surface between the lands by adding 1-2 mg/1 lead ions as lead nitrate. The Pb is co-deposited with the Ni during plating.

The lead ion (Pb++) content in the bath has to be maintained within a narrow concentration range. Too high a Pb content affects the Ni metallurgy; too low a content causes an unstable plating bath. To maintain the lead ion content within the low and narrow range would normally require frequent replenishment and analytical monitoring. The proposal suggests a means of maintaining the Pb content within the critical range for extended periods of usage without the need for replenishment or analysis.

In the proposed process the plating bath is brought into contact with a small supply of lead molybdate crystals suspended in the bath by means of an appropriate container. The molybdate is insoluble in cold water. However, in contact with a plating bath containing reagents which form tight complexes with Pb, the solubility of lead molybdate at room temperature is increased. Atomic absorption spectroscopy shows that the solution at room temperature contains about 8 mg/1 of lead ions. A corresponding amount of molybdate ions (6.2 mg/1) also goes into solution. At the normal plating temperature of 65oC in a bath in contact with solid lead molybdate, the lead ion content increases to 12 mg/1.

The amount of lead ions can be lowered by increasing the molybdate ion concentration. Adding 21.3 mg/1 ammonium paramolybdate to the bath lowers the lead ion content from 12.0 to 1.8 mg/1 at 65~C. This is i...