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PCB-Sept2017

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52 The PCB Magazine • September 2017 ing on technology of the design. A typical fab- rication panel will be 18" x 24" or 21" x 24". As technology requirements increase, the pan- el size used will decrease. Panel size is typically reduced to 12" x 18" when tight features are re- quired or when the process requires tighter reg- istration than standard processing is expected to meet. With the smaller panel size, there is less impact from standard material movement. When processing on a 12" x 18" panel does not yield the anticipated results due to materi- al movement, process engineering may suggest using the center or "sweet spot" on the panel to minimize that impact even further. Processing Thin Materials Again, this is an area that both fabrication and EMS work their magic behind the curtain. From the EMS perspective, PCBs that are less than 0.031" thick or flex materials require ad- ditional support for processing. Thin materi- als will flex and move during component place- ment and reflow. A common method to stabi- lize the array is to create a SMT pallet. Pallets will cycle through and be reused in the process. The number of pallets needed is determined by the manufacturing lot size and SMT cycle time to ensure proper manufacturing flow is main- tained. SMT pallets must be made to withstand high temperatures and cannot conduct heat allowing them to go through the reflow process. CDM Durapol ESD is a commonly used composite material that can withstand the high tempera- tures and includes static dissipative characteris- tics. Tension pins are designed into the pallet to align with the tooling holes on the PCB panel, securing the board in place through processing. THE MAN BEHIND THE CURTAIN Figure 1: PCB panel design aids in manufacturing processes throughout the factory.

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