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KICstart Version 1.1.0.x
KICstart User Manual 47
The third benefit is that because the PWI reflects the performance of the whole profile, it provides much
better indicator of process capability than tracking a single statistic. The PWI thus provides excellent data
for SPC and other QC monitoring programs while simplifying data gathering and reducing process
monitoring costs.
Finally, the PWI gives users a simple method for comparing thermal process performance. Comparisons
may be made between individual lines on the shop floor, between processes at multiple plants, and between
processes using dissimilar equipment. The ability to quantify thermal process performance will give
electronics assemblers a means for comparing the performance of their soldering equipment. This will be
of value in selecting equipment, for buy off, and for process troubleshooting.
Table 2 (below) is the result of a series of tests comparing oven performance using several sizes of PCBs.
Each board was profiled in the given oven, and then an automated profile prediction tool was used to find
the optimal profile for that board in the given oven. After the oven set points were changed and the oven
stabilized, a second profile was run to confirm that the predicted PWI had been achieved. The table below
shows that there is significant variation in oven performance between various makes and models. In this
test, Oven C had more zones than Ovens A and B, and performed better, as would be expected.
Table 2: Comparison of Oven Performance — Best Achievable PWI
Oven Board Type
Manufacturer Model Motherboard Cell Phone
Display
Adapter Mainframe
A X PWI = 87% PWI = 62% PWI = 79% PWI = 126%
B Y PWI = 71% PWI = 58% PWI = 61% PWI = 93%
C Z PWI = 33% PWI = 29% PWI = 34% PWI = 58%
Conclusion
The simplicity of the Process Window Index makes its validity as a statistical tool readily apparent and its
adoption as an industry standard clearly offers a significant opportunity for the improvement of the
soldering process. The advantages detailed above point to its value in demystifying the soldering process
and open the door to precision control of a process that has been ignored for too long. Issues like the
coming of Lead-free electronic assembly mean that electronics assemblers can no longer be complacent
about their soldering process. Sophisticated tools utilizing the PWI as a standard for accurately measuring
the thermal process will mean more efficient production, improved and simplified process control, and
higher quality final product.