How to avoid PCB delamination during manufacturing?

What is PCB Delamination?

When a PCB experiences delamination, the layers of base material begin to separate from each other. If viewed on a fabricated bare PCB or a fully assembled PCBA, the solder mask could appear to have large regions of discoloration and bubbling when delamination has occurred. Related forms of delamination are also known as blistering and measling. The former is nearly the same as large-scale delamination, while measling is the formation of very small delaminated white spots.

An example image showing delamination on the surface layer of a PCB is shown below. The somewhat-circular discolored area is where the top layer of materials are beginning to separate from the base material.

Figure 01:This image shows delamination occurring on the rigid regions of a flex cable.
The two main factors that can lead to delamination are moisture exposure and repeated thermal excursions.

Prevention Begins With Your Manufacturer

As is usually the case with other manufacturing defects, there is no single cause of delamination. The factors listed above work together to cause delamination and produce the defect shown above. The solution to remove moisture is pre-baking the PCB base materials before fabrication, and possibly before assembly. Baking the material slightly above the boiling point of water in vacuum will force water to desorb from the base materials without activating DICY/phenol curing agents.

It is the job of the fabrication house to ensure materials are stored properly and the proper material pairings are made when planning the stackup for fabrication. The assembler needs to ensure the reflow profile is properly selected so that thermal excursions do not repeatedly exceed the laminate’s Tg value. Finally, a pre-bake step may be needed before fabrication and assembly just to ensure any remnant humidity is removed from the base materials and the assembled board.