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Question My company assembles its own live devices and then encapsulates them with our molding compounds and subject them to environmental conditions to test the robustness of the materials. I am concerned with the possibility of ESD damage during the molding process. We take relative measures to protect the devices before molding by using static dissipative mats, ground straps and a 50% RH controlled environment. This includes die bonding and wire bonding of the devices. They are then stored in static dissipative bags in a nitrogen purged desiccator until molding. Here ends the ESD control. Questions: Are the devices safe from ESD damage as wired devices while being handled during the molding process? We feel they are safe because until the trim and form process, the leads of all the devices are connected by a common conductive frame. How can we protect them during the trim and form process? How can we protect them after the trim and form process when they are placed into a HAST chamber at 158 deg C. and 85 %RH. We use stainless steel cups to hold the devices during the environmental testing. When they are removed, they are placed on a conductive mat with air blown across them to dry them off before parametric testing. Any suggestions for improving the ESD control are appreciated. - Anonymous, Olean, NY
Answer As long as all the I/O inputs/outputs to the device are shunted (shorted) together to a common point and this point is not subjected to significant potential differences and is handled using ESD protective measures as you described in your ESD Control program, then the device should be relatively safe during the molding process. During the trim and form process, it is still advisable to utilize your ESD protective measures, where the operators are grounded via wrist straps and the work mat is dissipative and grounded to the same ground. If the materials used to encapsulate the device are insulative and can't be grounded, you may need to employ ionization. To determine this, you will want to measure the electric fields present with a field meter and compare them to the devices ESD Sensitivity classification. Make sure the stainless steel cups are grounded and that the devices are handled by a grounded operator before the device is placed into or removed from the cup. Ionization may be needed again for this operation, dependent on the fields that can be generated on the device's encapsulation if insulative.
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