SMTA International Conference Proceedings


STENCIL PRINTING SOLDER PASTE AND TRANSFER EFFICIENCY - ESTABLISHING THE BASELINE

Author: Jeffrey D. Schake / Mark A. Whitmore
Company: DEK USA / DEK UK
Date Published: 9/26/2004   Conference: SMTA International


Abstract: This stencil printing study introduces a novel measurement technique that uses reflowed solder bump height measurements on non-patterned silicon wafers to establish baseline paste transfer efficiency curves as a function of area ratio. By using bare silicon wafers as a general test vehicle, the dependence for the stencil to match a particular stencil pattern is decoupled, allowing unlimited combinations of uniquely designed non matching stencils to be tested in side by side solder paste transfer quality comparisons.

The experiments performed confirm that paste transfer efficiency performance is significantly influenced by the ratio of surface areas the solder material contacts in the aperture, known as area ratio. Direct comparisons of paste transfer efficiency between square and circular apertures across a broad range of equivalently designed area ratios resulted in similar performance indicate the circle may have the advantage.

Finally, detailed stencil aperture size measurements revealed important discrepancies between designed and actual values that weigh heavily on experimental conclusions and transfer efficiency expectations.

Key words: stencil printing, solder paste, transfer efficiency, area ratio.



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