Authored By:
Dr. Rita Mohanty
Speedline Technologies, Franklin MA USA
Rajiv L. Iyer, Daryl Santos
Binghamton University, Binghamton, NY USA
Summary
Stencil printing technology has come a long way since the early 80's when SMT process gained importance in the electronics packaging industry. In those early days, components were fairly large, making the board design and printing process relatively simple. The current trend in product miniaturization has led to smaller and more complex board designs. This has resulted into designs with maximum area utilization of the board space. It is not uncommon, especially for hand held devices, to find components only a few millimeters from the edge of the board. The board clamping systems used in the printing process have become a significant area of concern based on the current board design trend.
The primary function of a clamping system is to hold the board tightly in place to provide optimum gasketing during the printing process. There are various types of clamping systems available in the market, including top clamp, snuggers, flippers, and vacuum hold down.
Top clamp and snuggers, two primary clamping systems, operate slightly different in providing the mechanism to hold the board. Top clamp, as the name implies, holds the board in place by applying a clamping system (a thin metal foil) on the top of the board. While the snugger works by tightly snugging the board in the Y direction without any foil on top of the board.
The current study is designed to investigate the effect of top clamp and Y-snugger on both a specially designed test stencil and production quality cell phone boards. This study will use a 3D Solder Paste Inspection (SPI) system to determine the variation in paste volume and height based on the location of the pad on the board. Various statistical techniques will be used to analyze the SPI data to determine the effectiveness of the clamping system.
Conclusions
Two sets of experiment were conducted to understand the effect of rail clamping systems on overall print quality of solder paste printing. Two different types of clamping systems were used herein, MPM's TopClamp and EdgeLoc. The baseline test, which used a special stencil design, showed that the EdgeLoc system has less variation in TE than the TopClamp system. This is due to the smoother transition of squeegee blade over the clamping system during a print stroke. The second test, which used a production quality cell phone board, confirmed that the EdgeLoc system provides better gasketing and hence better overall print quality.
In addition, it is observed that for fine pitch components, the effect of clamping system is even more critical. The EdgeLoc clamping system provided higher TE with lower standard deviation. Based on this study, it can be concluded that the EdgeLoc clamping system is a more desirable clamping mechanism, especially when using fine pitch components.
Initially Published in the IPC Proceedings
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