Effects of Electronics Assembly Processes on Benzotriazoletreated Printed Wiring Board Copper Surfaces.

Abstract

The performance and reliability of personal computers, workstations and other electronic products depend on the effective soldering of electronic components to printed wiring oards (PWBs). The copper surfaces of PWBs are frequently treated with benzotriazole (or similar organic complexes) to preserve solderability by preventing copper oxide formation. However, new assembly process techniques and more complex processes may degrade protective organo-copper surface complexes and allow copper oxidation to occur, thus inhibiting subsequent solder operations. This study uses Auger electron spectroscopy (AES) in conjunction with meniscograph wettability results to determine the effects of processing conditions on the solderability of PWB surfaces. Effects are characterized for aging up to 19 months; Infrared (IR) reflow in air and nitrogen; cleaning; and temperature cycles associated with adhesive or encapsulant cure. Surface compositions, oxide thicknesses, and solderability measurements are correlated to the above process steps. For example, IR reflow in air increases oxide thickness from ≈10 Å to ≈150 Å (relative to sputtering rates in Ta₂O₅ with an attendant increase in the meniscograph time-to-neutral-buoyancy from <2 seconds to >10 seconds, relative to unprocessed PWBs. Such fundamental information serves as an invaluable complement to standard phenomenological observations of defective solder joints, and can aid in guiding processing decisions for improved yield and reliability.