One-piece interconnection package and process

Abstract

A one-piece interconnection structure (10) for an SO package (60) is formed from a single sheet strip (12) of copper having a thickness of about 8 mils. Contact finger patterns (14) are formed from a plurality of contact fingers (22) which extend in cantilever fashion. The fingers (22) have tips (24) of a reduced thickness of between about 2-3 mils. Stress relief slots (26) having a depth of about 2 mils are formed in the underside of each finger (22) spaced back from the tips (24) to give the fingers increased flexibility for downward bending during assembly operations. Vertical slots (28) on opposing sides of the fingers behind the stress relief slots give increased lateral flexibility to the fingers. Steps (30) extend vertically along the lateral fingers (22) and have two surfaces (32 and 34) angularly disposed with respect to central surface (36) on the top and bottom fingers. In combination, the stress relief slots (26), vertical slots (28) and the different configuration of the steps (30) make the fingers (22) have the same flexing characteristics in response to bending forces on them, even though the fingers (22) have different shapes depending on their positions in the finger pattern (14). The contact fingers (22) and the reduced thickness tips (24) are formed by masking strip (12) with photoresist in patterns on the top and bottom of the strip to define the contact fingers, but leaving the strip exposed on its top surface where the reduced thickness tips are to be formed, and directing spray etchant at the top of the strip and at the bottom of the strip at different pressures.