SMT007 Magazine

SMT-Jan2016

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January 2016 • SMT Magazine 73 up and the project is running approximately 30,000 PCBAs per month. There are some tradeoffs that can be easily dealt with once a team becomes familiar with the process and the technology. One technical challenge with VP reflow soldering is that the process can exacerbate 0402 and smaller device tombstoning. The solution is to incorporate a reverse home plate design for those pads on the stencil. Another issue is the efficiency of the vapor blanket. In the 1970s and 1980s, when VP was still a common option, one of the negatives as- sociated with VP technology was the fact that hybrid parts could be heat damaged. Sealed parts with open cavities could expand or explode. DC to DC or AC to DC converters (hybrid potted modules) would often fail. Today's technology minimizes those parts, but profile optimization is important because both sides of the PCBA go into reflow instantaneously. A key selling point of the technology is that the process windows are broad enough that few unique profiles are needed. However, there can be a learning curve in developing the right pro- file because of the speed at which reflow begins. For example, the engineering team once ruined a profiler because the process was set at a level where the electronics inside the mole reflowed while taking measurements. The Cost Savings Equation VP reflow technology can save cost in sev- eral ways. First, it uses less energy than convec- tion reflow soldering systems, in part because it doesn't radiate excess heat. It not only uses less energy, but the factory also requires less energy for cooling the air near the machine. For ex- ample in Mexico, where summer temperatures routinely exceed 100°F, VP is 40% an hour less expensive than use of a nine-zone convection reflow oven just in machine energy consump- tion alone. Add to that the fact that energy costs in Mexico are 1.5x higher than those in the United States and the additional savings associated with less radiant heat, and the con- comitant load that places on air conditioning utilization, add up quickly. One area that adds cost is the fluid used to generate the vapor blanket since it is a consum- able. However, the cost of the fluid is near or below the cost of nitrogen frequently used in convection reflow ovens. One other area where VP reflow solder- ing technology can save money is on mixed technology PCBAs. When there are only a few through-hole parts, the PCBAs can often be completely soldered using pin-in -paste and VP technology. Depending on the product mix, this can eliminate or reduce the need for selec- tive soldering systems or wave soldering ma- chines. Additionally, while wave solder is typi- cally a 3 Sigma process, SMT reflow is a 5 Sigma plus process, which means that the SMT pro- cess is much more repeatable and controllable in volume production. VP reflow soldering technology has ma- tured to the point where it can easily support higher volume production requirements. The challenge is properly sizing the machine to likely workloads and optimizing the necessary profiles. The end result is improved quality, better line flexibility and lower energy con- sumption. SMT VaPOr PHaSE TECHnOLOGy IS a VIaBLE SOLuTIOn, BuT CarrIES a LEarnInG CurVE ArTiClE figure 3: X-ray image showing consistent ball shape and solder wetting from vapor phase reflow. Steve Fraser is vp of operations at firstronic. He can be reached at sfraser@firstronic.com.

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