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The Application of the Pin-in-Paste Reflow Process

The Pin-in-Paste (PIP) reflow process, also called through-hole (TH) reflow or pin-in-hole (PIH) reflow technology, has become more popular because it eliminates time-consuming processes, such as hand and traditional wave soldering, without losing the advantages that through hole components can offer.

The benefits of the pin-in-paste reflow process include:
  1. Use of the same SMT equipment for both SMT and TH components
  2. Elimination of hand and wave soldering processes
  3. Reduction of machine setup time
  4. Reduction of production turn around space and time
  5. Elimination of the board cleaning process since it is unnecessary to clean TH components
The pin-in-paste reflow process is similar to the SMT reflow process in the following way: Printing solder paste around the through holes first, inserting component pins to relative PCB holes and then sending it to the reflow oven to cook. But, in reality, the pin-in-paste reflow process is not as simple as the regular SMT process. A process engineer needs to evaluate the TH components’ ability in the following way:
  1. Are the components PIP ready?
  2. Not all TH components, especially the connector’s plastic housing, can withstand reflow temperatures up to 260°C over several seconds. The component’s geometry such as pin length and free space also need to be reviewed in order to make the right decision.
  3. Is the layout designed for the PIP process?
  4. If the PCB hole diameter is too big, it will require too much solder to fill it up. If it is too small, it is very difficult to fill the hole properly with paste during solder paste printing. Also, low solder volume can cause solder defects.
  5. Is the stencil designed for the PIP process?
  6. To get enough paste to fill up the pin hole, the stencil aperture must be designed bigger than the solder pad size depending upon the paste volume calculation.
  7. Is reflow profile optimized for the PIP process?
  8. Consider a delta type reflow profile first in order to reduce most of the defects. This profile has a slow ramp up of 0.5 to 1°C per second, a slight dwell at the liquidus temperature, a minimum time above liquidus, and a rapid ramp down of 4° C per second or less.
Finally, you should perform experiments as part of the evaluation process.

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