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A solder paste inspection system was used to analyze the solder paste distribution from the printing process, and an interesting observation was made during this analysis. Figure 6 shows the distribution of all of the m03015 pads during this testing. The data clearly shows that there are two distributions included in the dataset.
Figure 6: Solder paste data for all m03015 pads.
Looking at the data, there are two distinct sets of distributions included. After further analysis, it was found that the pad designs on the test board were done differently. The 200- and 150-µm pad designs were done with the solder mask throughout the array of pads while the 100-µm pad area had solder mask completely cleared from the pad area (Figure 7).
Figure 7: Solder mask differences in 200-, 150-, and 100-µm pad areas (L to R).
The data was separated into the two types of pad designs, and the distributions were redone. Figure 8 shows the new data.
Figure 8: Cpk analysis for each set of pads (solder paste volume).
The Cpk data looked good with 1.71 for the 200- and 150-µm pads and 1.62 for the 100-µm pad area.
Pick-and-place Operations
We then proceeded into the pick-and-place operations. Initial verification was done on double-sided tape. An issue was found where some of the initial placements damaged the component. Figure 9 shows where the component impacted the board with too much force and shattered it.
Figure 9: Damaged component during placement.
Everything was checked, the placement force was set at a minimum, and this was still seen. It turned out to be a software bug where the height the placement head started its deceleration was not set properly. This only happened on the first placement of the board. This has been resolved since this time. Then, the placements on solder paste were then done with 100% visual inspection to verify placements. No defects were found at any of the spacings—just the initial placement as previously seen. Figure 10 shows a sample of the components placed onto solder paste.
The pick-and-place rates were recorded; the pickup rate was 98.9%, while placement rate was 100%. These results were very encouraging because the rates were in the expected areas, and that the equipment could tell if a part was present on the nozzle or not. Most of the latest equipment does this well.
Figure 10: Component placement on solder paste.
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