Any shielding on the PCB should have an equal effect along the joint area. This design will act as a thermal dam, preventing excessive heat drain from the pad area during the hot bar reflow soldering process.įor multi-layer boards, restrict the traces under the bonding area to the smallest width possible and spread equally under the pads on the PCB. Note that the traces leading from the pads should be of equal width and be as narrow as possible. Equally sized small traces act as a thermal dam and ensure equal heating across joint area. The cooling slope rate should be about twice the preheat slope rate to avoid PCB parts bending and burrs on the solder joints. 0.08” is the effective minimum area in which there must be no heat sinks if small trace heat dams are used.Į. The reflow cooling stage is the step where the solder consolidates as the reflow oven zones' temperatures get down from the peak to 75C, and the components and PCB pads are well soldered. Offset caused by solder paste collapse 6. Reduced-width trace acts as a thermal dam and prevents any heat sinking of the pad.ĭ. The flux content is too high, the flux will boil during reflow soldering, and the SMD will move on the liquid flux 5. Increased trace width and plated through-hole draw heat from the joint area.Ĭ. Heat is transferred away from the joint area to the large pad area, which is positioned too close to the joint area.ī. Reflow This is the stage where the temperature within the reflow oven is increased above the melting point of the solder paste causing it to form a liquid. Lets go through the different processes between reflow soldering and wave soldering below. Small differences may not have much effect on quality, but any large thermal mass change along the joint area will cause inconsistency of temperature and result in a poor solder joint.įollowing are some of the common part design problems we run into and possible solutions to ensure successful hot bar bonding.Ī. In modern electronics manufacturing where components sizes are increasingly miniaturized, it is common to use only reflow soldering or both reflow soldering and wave soldering for PCB assembly. When the temperature reaches that value the reflow process begins with a set temperature for a brief amount of time (about 180-200☌). First one is the preheat where the whole board rises towards a certain temperature (about 120-150☌). Then the heater starts and the PID algorithm starts controlling the temperature. There are 3 stages of this reflow soldering process. Here you can see the graph based on the reflow profile that we have set in the code. Heat sinking differentials along the solder joint length are the most common design problem to overcome. Why PCB delaminate during reflow soldering. The reflow process starts when we press the start button. Excessive differences in the heat sinking capability of the two parts being joined can also cause solder cracking during cooling. But some materials – ceramic substrates in particular – need to be heated in a more controlled fashion to minimize the chance of cracking. Most PCB materials like FR2 and FR4 are very resilient to the application of heat during the hot bar reflow soldering (or hot bar bonding) process.
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