DEK releases new mass imaging processes

DEK's process for B-stage epoxy deposition allows application of die attach adhesive at the wafer level, at high rates of throughput. This streamlines package assembly and also allows OEMs to outsource this process to a wafer specialist, if required. DEK's B-stage epoxy deposition process is capable of depositing a part-cured adhesive layer of nominal thickness 50 micron, with TTV less than ±5 micron, across the entire back-side of the wafer. Traditional wafer coating methods cannot match this combination of uniformity, repeatability and high throughput. For attaching singulated die to a lead-frame or bond pad, DEK's new mass imaging process replaces dispensing as the means of depositing silver-loaded wet epoxy ahead of die attach. Many hundreds of deposits can be made simultaneously, which for the first time enables epoxy deposition to match the speed of die placement. Die placement rates are now moving beyond 40,000 units per hour, leveraging SMT pick and place technology. In addition, DEK's mass imaging process for wet epoxy also provides greater control over the volume and shape of the deposit, by optimising the stencil aperture. During the project, DEK engineers identified a star-shaped epoxy deposit as the optimum shape for effective die attach without producing an excessive fillet, which may contaminate the die surface. Large numbers of star-shaped deposits can be created simultaneously using screen printing. Using a dispenser, a sequence of several dispense operations would be necessary to create each deposit, which is slower and less repeatable. “Mass imaging delivers the throughput, uniformity and repeatability that commercial producers of advanced semiconductor packages need in order to economically meet market demands for quality and price,” said Clive Ashmore, Global Applied Process Engineer at DEK. “For die attach using B-stage or wet epoxy adhesives, our mass imaging processes outgun legacy techniques in every respect, to deliver a more highly optimised, faster, more repeatable and more cost-effective solution.”