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Arm Yourself Against PCB Defects

The OEM drive to better, smaller, more complex, and higher performance PCBs is taking its toll on quality and reliability unless the EMS provider’s design and assembly team continually stays on top of the newer PCB technologies that are increasingly being used.

Different solder defects and related failures are surfacing more due to smaller boards and shrinking ball size and pitch of ball-grid array (BGA), chip-scale (CSP), and quad-flat no-lead (QFN) packaging.

For example, today’s highly advanced BGA packages are fitted with tiny balls ranging from 0.15 to 0.25 millimeter (mm) in size, according to Institute of Printed Circuits (IPC) literature. BGA ball pitch, on the other hand, ranges from a standard 0.8 to more advanced 0.25 mm pitch. Pitch is defined as the spacing between the center of one BGA ball to the center of the next one. As a result, there’s very little area left for the soldering process.

Fig-1-Shorted-bga-balls (1)The main defects due to inadequate board design and assembly include shorts, opens, bridging, tombstoning, cracked BGA balls, head-on-pillow and BGA intermittent connections, among others. For example, Fig. 1 shows a BGA short that’s defined as a defect occurring when placing too much solder paste on a BGA ball.

These defects and reliability issues result from poor solder paste deposition, stencil quality, less than perfect thermal profile, inadequate assembly and inspection systems, out-of-date assembly floor personnel training and a lack of collaboration between PCB designer and assembly/manufacturing engineering.

To get more details, take a moment to read our latest article in EE Times on this issue.

It’s always a good idea to arm yourself with sufficient know how to guard against these defects, especially if your next PCB project is based on leading-edge technology. Here are some tips and hints that’ll help you along this route.

  • Understand that your PCB designer should be seasoned enough to maintain close collaboration with his/her assembly/manufacturing engineers to minimize or eliminate defects.
  • Make sure tight assembly processes are specified when your PCB project is densely populated with 0201 or 01005 packages.
  • Ensure your PCB designer knows the limitations of various fabrication and assembly process machines.
  • Avoid hand placement of components as much as possible since this is the basis for reliability issues leading to defects.
  • Check on training and experience levels to ensure your design can be manufactured.
  • Ask your EMS provider about stencil thickness for your PCB assembly. The wrong thickness can lead to depositing too much paste causing shorts on 0102 components.

Besides the critical collaboration between PCB designer and assembly engineering and high-caliber, up-to-date training, it’s also important for PCB designers to get an understanding of today’s laser solder paste height inspection systems or SPI. This is the third major part of minimizing defects and involves using effective SPI systems operated by highly trained technicians.