How to print solder paste on PC Board and screen printing notices?

Printing the solder paste on the PCB (Printed Circuit Board) and go through reflow oven to re-melt the solder paste and solder the electronic components on PCB is most common process in today’s electronics manufacturing industry. Printing the solder paste on the PCB just like painting on the wall. The only different is solder paste printing ask more accurately position and must control the solder paste volume on each pad. It requires a certain jig call “stencil”  is a sheet-metal made and have designate aperture on the position that needs to print solder paste.

Almost of current PCB assembly manufacturer apply the “stencil” jig to enhance the solder paste printing process to get more accurately printing position of solder paste and control the solder volume. Once the solder paste print shift from its pad too much then the solder will not joint the electronic component and PCB pad together. The solder paste volume over or less quantity will make solder short or open defect.

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Increase solder paste volume will improve the MLCC capacitor broken?


Recently WorkingBear got complaint from R&D and ask increase the solder paste volume on the MLCC (Multi-Layer Ceramic Capacitor)  component pads to improve the capacitor broken issue. R&D said he had verified that the capacitor’s footprint in the board design is correct and followed manufacturer’s design guidelines. However, looks like there is not enough solder paste to form proper heel fillet on the terminal of capacitor. This insufficient solder paste volume make the solder cracking?

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Comparison between shielding-can directly mount and shielding-clip/frame

Recently one of my top manager ask to mount the shielding-can or call shielding-cover directly on the Printed Circuit Board to instead of mount the shielding-clip or call shielding-frame on the board first then cover the shieling-can. He said this “new process” is more cheap and can reach better RF (Radiation Frequency) performance. Also most of current popular cell phone board apply this solution.

Well, I must say yes. Directly mount the shielding-can on the board is cheaper and save labor hours as compare it with mount one component (frame or clip) on the board first then install another component (can or cover) to cover it. But this new requirement also got lots of negative feedback from SMT factory and repair center. Because of directly mount shielding-can on board means that repair guy must de-solder the shielding can first before repair the component under the shielding can. It make the repair job more difficult and may give more trouble and damage the board during repair.

Related article: The benefit to use shielding clips to instead of shielding frame

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Trouble Shooting Guide for Plastic Injection

Trouble Suggested Remedies (Solutions)
Shot-to-shot dimensional variations
  • Increase injection pressure
  • Maintain uniform pad (cushion)
  • Repair leaking back flow value if pad cannot be maintained
  • Increase screw forward time
  • Maintain uniform cycle
  • Eliminate un-melted particles (see below)
  • Use larger machine or screw designed for DELRIN
  • Balance mold temperature
  • Decrease mold temperature
  • Increase/decrease screw forward time
  • Increase/decrease injection pressure
  • Clean water channels in mold; improve mold cooling system
  • Improve part design
  • Change or add ejector pin locations

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Solution to the Drop of First-Side Part during the Second Reflow Soldering

Solution to the Drop of First-Side Part during the Second Reflow SolderingFirst of all, with the rapid growth of mobile phone technology, the Electronic Manufacturing Service (EMS) in mainland China sometimes meet serious labor shortage. Second, the Industry 4.0 promotes the requirement of factory automation for each EMS. Therefore, many parts which cannot adopt SMT reflow process are requested to fulfill Paste-In-Hole process (PIH process), such as the type-A USB connectors, Ethernet connector, power supply sockets, transformers, and so on. Originally, most of these kind of devices were touch-up soldered after SMT process.

Because of labor shortage, also for the purpose of saving process cost, and under the consideration of quality, many SI and EMS have requested that the parts which cannot adopt SMD process should fulfill at least PIH process, so that the soldering of all the electronic parts on circuit board can be completed after SMT process.

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