Article: Electronic Specifier
Sensor Film Minimizes Defects and Improves Quality in Wafer Bonding
Pressurex® surface pressure indicaing film from Sensor Products Inc. is a quick, accurate and economical way to detect and correct pressure variations which can result in flaws (defects) in the wafer bonding process. When placed between contacting surfaces, it instantaneously and permanently changes color directly proportional to the actual pressure applied. With Pressurex®, variations in pressure that lead to imperfections (or irregularities) in the bonding process can be accurately detected and corrected -- improving yield, decreasing scrap, and boosting productivity.
Pressurex® can used in virtually any application where two surfaces contact each other. Applications include materials testing, composite lay up, fuel cell stacks, heat sinks, pcb lamination, clamping, bolted joints, heat sealing, converting, die extrusion, injection molding and countless others.
In wafer bonding, two flat substrates are permanently joined together by applying carefully calculated pressure, temperature, and voltage. Of the three parameters, pressure is often the most difficult to precisely ascertain and control. Traditional methods assume perfectly flat pressure plates. However, in nearly all real environments pressure plates are not ideal due to manufacturing or installation variability and degradation over time from wear. The result is difficult to detect pressure variations across the surface that can lead to un-bonded wafer areas, cracked wafers, and premature wear of the pressure plates.
Bond Tool Images Show Improvement to the Pressure Uniformity as Captured by Pressure Indicating Film
Pressurex® systematically measures pressure across the entire pressure plate. It is a mylar based film that contains a layer of tiny microcapsules. The application of force upon the film causes the microcapsules to rupture, producing an instantaneous and permanent high resolution “topographical” image of pressure variation across the contact area.
When placed between contacting surfaces of the wafer bonding fixture, the film instantaneously and permanently changes color directly proportional to the actual pressure applied. Precise pressure magnitude is easily determined by comparing color variation results to a color correlation chart (conceptually similar to interpreting Litmus paper). The film’s thickness is 4 or 8 mils, which enables it to conform to tight spaces. It is ideal for invasive intolerant environments and tight spaces not accessible to conventional electronic transducers. Additional pressure analysis of the film is available through Sensor Product’s Topaq® Imaging System which assimilates the pressure distribution into 2-D and 3-D pseudo color images, histograms and line scans among other features.