Thermosonic Wire Bonding On Single-Layer Polymer Hybrid Integrated Circuits (POLYHICs)
01 January 1986
A study was undertaken to evaluate the thermosonic gold-wire bonding capability to Ti-Pd-Cu-Ni-Au thin film metallization on newly developed polymer hybrid integrated circuits (POLYHICs). (The POLYHIC technology incorporates alternating layers of polymer and metal added to conventional Hybrid Integrated Circuits which provide for increased interconnection density.) Destructive wire-pull strengths were measured as a function of varying wire-bonding machine operating parameters of wedge bond force, wedge bond time, temperature, and ultrasonic energy. All data were evaluated and compared to wire bonding under similar conditions to thin film circuits on Al sub 2 O sub 3 ceramic. The results for wedge-bond associated failures indicated that machine operating parameters of wedge bond force, time and ultrasonic energy similarly affected the average wire-pull strength for both the ceramic and POLYHIC circuits. Pull strengths for equivalent metallization schemes abd bonding parameters were generally slightly higher and more tightly distributed for bonds made to metal films on ceramic. A strong correlation was found to exist between wire-pull strengths and surface topography (as measured by a profilometer technique) of the thin film metallization for the POLYHICs which had both smooth and rough metallization surfaces for metal films on top of the polymer. The results indicated that rough metallization bonded more easily and yielded much higher wire-pull strengths. Also, rougher films were shown to effectively increase the parameter-operating windows for producing reliable wire bonds. A semi-quantitative analysis was developed to help explain this correlation. Surface topography effects were also found to be a key factor when evaluating wire bondability as a function of substrate bonding temperature. Wedge-bond strength was essentially independent of temperature for bonds made to rougher metallization while a strong temperature dependency was found when wire bonds were made to smoother films.