Surface Mount Technology (SMT) experiment - problem solving in a manufacturing environment 2 types of defects, probably related - Solder balls - Solder-on-gold Statistician invited in for a “quick fix” experiment High volume memory card product

Problem in screening / reflow operations Prep card Solder paste screening Component placement Solder paste reflow Clean card Inspect (T2) Inspect (T1) insert

8 potential process factors Clean stencil frequency: 1/1, 1/10 Panel washed: no, yes Misregistration: 0, 10 ml Paste height: 9ml, 12 ml Time between screen/ reflow:.5, 4 hr Reflow card spacing: 18 in, 36 in Reflow pre-heat: cold, hot Oven: A, B

Experiment design conditions Resources only permit 16 trials Get efficiency from 2-level factors Measure both types of defects Introduce T1 inspection station for counting defects Same inspectors Same quantity of cards per trial

Can we measure effects of 8 factors in 16 trials? Yes

7 more columns contain all interactions Each column contains confounded interactions

Normal plot for factor effects on solder ball defects C D CD

Which confounded interaction is significant? AF, BE, CD, or GH ? The main effects C and D are significant, so engineering judgement tells us CD is the true significant interaction. C is misregistration D is paste height

Conclusions from experiment Increased paste height (D+) acts together with misregistration to increase the area of paste outside of the pad, leading to solder balls of dislodged extra paste. Solder ball occurrence can be reduced by minimizing the surface area and mass of paste outside the pad.

Implemented solutions Reduce variability and increase accuracy in registration. Lowered solder ball rate by 77% More complete solution: Shrink paste stencil opening - pad accommodates variability in registration.

The Power of Efficient Experiments More information from less resources Thought process of experiment design brings out: –potential factors –relevant measurements –attention to variability –discipline to experiment trials