SMT007 Magazine

SMT-Jan2016

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72 SMT Magazine • January 2016 Comparatively, convection reflow oven stabi- lization can add as much as 15 minutes to a changeover process. That said, VP reflow is a batch process and throughput can't be changed. While that works well with the smaller lot size focus of Lean, the system can become a constraint if sized below the likely line volume. For example, Firstronic selected an IBL CX600 VP reflow soldering sys- tem when it added the technology in Novem- ber 2014 because the facility was ramping pro- duction and a conservative approach seemed justified. The machine is sized for medium- to high-volume production environments, which typically would have no more than two SMT placement machines feeding the reflow process. When the second system was added in mid- 2015, a higher volume CX800 system was se- lected because production volumes had grown faster than anticipated. SMT line configura- tions included three SMT placement machines and the smaller CX600 system was becoming a constraint. The larger system supports the three placement machine configuration with no throughput issues. Significant Quality advantages VP reflow soldering involves immersing PCBAs in a vapor blanket. This contributes to even heating and the vapor penetrates under every component. From a quality standpoint, this vapor blanket ensures perfect wetting and void-free, high quality solder joints. It also pro- duces cleaner solder joints at lower tempera- tures (typically 240°C), eliminating the defect opportunities that can be caused by thermal shock during a convection reflow process that may reach 270°C. The use of VP reflow soldering technology can result in immediate yield improvements over convection reflow processes. For exam- ple, this contractor's Mexico facility produces a PCBA which is also produced in China. The PCBA has microBGAs on both sides, including two microBGAs on the bottom side and seven microBGAs/BGAs on the top side. The largest BGA package has 266 balls. There is one chip scale package on each side of the PCBA. The 14-layer, high temperature FR4 OSP PCBA has 1809 components. In Mexico, VP reflow solder- ing is used, and convection reflow soldering is used in China. BGA opens/shorts are the num- ber one issue in China, while the Mexico facil- ity has experienced no solderability issues. In another case, the facility is producing large PCBAs used in flat panel monitors. In con- vection reflow soldering a large PCBA can see as much as 90°C variance in temperature from one end of the PCBA to the other as it moves through various zones. If all parts are sitting in solder paste, this doesn't cause an issue; how- ever, if balls aren't touching paste this thermal mismatch can cause parts to pitch slightly and form a gas bound- ary which causes an oxi- dized "pillow" to form. The end result is that parts touch but don't reflow. In VP reflow sol- dering the difference in temperature from one end of the PCBA to the other doesn't exceed 2°C, eliminating the po- tential for this issue to occur. In this particu- lar project, the facility achieved yields of over 99% in the first three days of production ramp- VaPOr PHaSE TECHnOLOGy IS a VIaBLE SOLuTIOn, BuT CarrIES a LEarnInG CurVE ArTiClE figure 2: a vapor phase "blanket" provides even heating and the vapor penetrates under every component.

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