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Advanced Packaging Calls for Exact Reflow

Today’s shrinking component size is rapidly changing the reflow process. Take for example microBGAs defined in today’s technology as 0.4-millimeter (mm) pitch or smaller. Other smaller packages include 0402s, 0201s, 01005, CSPs, QFNs, and DFNs. But the extremely small leadless BGAs represent the greatest challenge to contract manufacturers (CMs) and EMS providers. These small devices are now making their presence known as a new technology, which is not well defined in terms of reflow process.

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The leadless BGA is smaller in size like a micro BGA. But unlike a BGA, which has balls to be soldered on the board’s surface, leadless devices have what are called ‘bumps.’ Those bumps are smaller in size to the tune of 30 to 50% smaller compared to BGA balls. This is the main reason a leadless BGA creates challenges and issues when it comes to printing and reflow.

Check the online September/October issue of I-Connect/SMT Magazine to get the latest details on how best to deal with advanced packaging and the right reflow process. In the meantime, here are some tips for you to follow to ensure your PCB project is properly assembled when you use advanced packaging.

  • Understand there are different re-work steps between conventional BGAs and leadless BGAs. Make sure your CM knows the difference.
  • Installing micro and leadless BGAs calls for calculating the amount of force on the Z-axis, as well as the X and Y axis.
  • Insist on well-trained technicians for the BGA de-population process to avoid unnecessary pad damage.
  • Ensure the CM has the latest inspection systems to uncover issues like head-on-pillow and BGA cold solder joints.
  • Keep in mind, all thermal profiles are not created equal. Reflow of your PCB project requires a custom thermal profile using the proper solder paste.
  • It’s best to have the CM use an InkJet technology printer for paste dispensing to maintain accurate control, Fig. 1.

It’s also important in the reflow process to 100 per cent match the chart that the solder paste manufacturer provides. For older device packaging, it may not be necessary to follow it 100 percent since some wiggle room exists for these reflows. However, when it comes to tiny leadless BGAs and QFNs, there is no room for error and those charts must be followed to the nth degree.