Aligner for Bump Bonding

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I have been developing an alignment device to make flip chip bump bonding. The main task of the device is to bring a pixel sensor and a pixel readout chip together precisely so that bumps on each of them make contact. Since bumps are usually about 20 microns in size and of about 100 microns in pitch which is a challenging task. A beamsplitter with one of the surfaces silvered is used to view both surfaces simultaneously. Precise linear bearings (kinetic movements in the fist prototype) were used for precise positioning. Beamsplitter was aligned first looking at a reticles which were known to be aligned well.

This is the first prototype built to test the feasibility of the divice. It was mostly made of scrap metal and scrounged parts, and I machined it myself at the student shop. Kinematic slides in the form of steel balls sliding on two metal rods were used to obtain backlash free linear motion. They were held together by permanent magnets. It worked as expected, and proved the the feasibility of the concept. more pictures

This was built to mount ball grid array type FPGAs (for the fabrication of prototype PCBs for the CMS pixel readout) as well as a learning exercise for a more precision aligner. It was machined at the physics department machine shop and used commercial linear bearings. Total material cost was about $2000. We used it to mount fine pitch pin FPGAs on the first prototype FPGA-TBM test boards. It also provided valuable experience for the next version. more pictures

This is the flip-chip bump bonder still under construction. Precision linear bearings and differential adjuster screws were used to obtain accurate alignment and control needed for bump bonding. It is work in progress, and few technical issues need to be worked out before it is ready for bump bonding.