IXYS adds Nikon Metrology X ray system to UK power semi production line
The current Press-Pack capsules from IXYS are clamped together under high pressure to achieve the required electrical rating, compared to the new isolated power modules on DCB (direct copper bonded) substrate technology. The Nikon Metrology XT V 160 is needed because the reflowed solder, which attaches the chips to their contact pads on the DCB, must be continuous with a controlled level of voids and X-raying is the only way to see if these conditions have been met.
“I previously used a smaller Nikon 130 kV X-ray quality assurance (QA) system when I worked at an electronics company in South Wales, so I knew how easy their equipment is to use,” said Fiona Lambert, Process Engineer at IXYS UK Westcode. “After reviewing what else was on the market, it was clear that their more powerful 160 kV model would best suit our application, which involves penetrating thicker and higher density materials to observe solder coverage.
“What I particularly like about the Nikon system is the easy access to the large stage, which allows me to place several, quite large components on it at the same time. The machine is fast in operation and the stage is easy to manipulate in multiple axes, so tilting, rotating and positioning as well as zooming the image on the screen is rapid. You can see everything clearly, as the image is high resolution. The software is also user-friendly and even works out automatically the percentage of voids in the solder, required to ensure the product meets rigorous specifications.”
The XT V 160 inspects the assembly reliably, even without an optional X-ray laminography software or CT (computed tomography) add-on. The 20W target power rating, focal spot size between 1 µm and 10 µm depending on power output, up to 36,000x system magnification and the high image quality from a Varex 16-bit flat panel allow easy distinction between geometrical shapes and the amorphous voids.
While the X-ray machine was installed specifically for DCB inspection, its presence on the Chippenham site has proved beneficial for verifying the quality of bought-in materials. On one occasion, a supplier disputed that there was a high incidence of solder blockages in a consignment of delivered coolers that form part of Press-Pack IGBT stacks. A simple analysis using the XT V 160 provided irrefutable evidence and resulted in the prompt arrival of a replacement batch.
The XT V 160 is an open-tube design so that replacement of the electron beam-producing filament can be scheduled a couple of times per year for a cost of a few pounds. Filament replacement takes minutes, so downtime is short. A sealed tube, on the other hand, will last for a couple of years but can stop working without warning, perhaps at the worst possible time for the user. The manufacturer then has to be called in to renew the tube at a cost of many thousands of pounds and the machine is down for days.
With one or two products per batch to be X-rayed for QA, the machine will be in constant use once the process has been finally established.
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