SOLDERABLE METAL FINICH FOR INTEGRATED CIRCUIT PACKAGE LEADS AND METHOD FOR FORMING

摘要

A packaged integrated circuit (10) includes a die (20) surrounded by an encapsulant (18) in which leads (14) are used to electrically connect the die, which is internal to the encapsulant, externally. The leads have a primary metal that is used for electrical conduction and physical support. The external portion (30) of the lead is coated with another metal, typically tin, that is useful for soldering. This tin layer (32) is formed in a manner that ensures that it is porous. Although porous is generally thought to be a bad characteristic, it turns out to be very effective in absorbing stress and thus retarding whisker growth. Whisker growth, which can short adjacent leads together as well as cause other deleterious effects, has been a major source of failures in packaged integrated circuits. An additional layer (36) of very thin tin that is non-porous can be added before or after the porous tin layer has been deposited.