Wire pull testing cannot be used to monitor wirebonding process control as the X-bar and R charts of raw pull strength data routinely demonstrate wide variations. The bonding process appears to be out-of-control, indeed the testing methodology and data collection itself are inaccurate in representing the process. Many factors, which are difficult to control in production, can subtly affect the raw data SPC. The author will review the pull test method to identify the potential variation (s), that causes the errors and are misleading in the process control. The paper also includes the efforts to revise the ASTM's method F. 459 for its Pull Test in making the data collected using this method applicable in the statistic process control (SPC) chart.
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