Fire on Multilayer PCB

Gideon Analytical Laboratories received a PCB that had a fire in one section of the board. These PCBs can provide high-performance 10G visibility for network monitoring tools in all parts of a fiber network. They feature to 24 SFP+ ports supporting 10G and 1G Ethernet (10GbE and 1GbE) and up to four RJ-45 copper Ethernet ports. The objective was to find the cause of the fire on the board, in an already established product line.

Most of the fire damage occurred under the two electrolytic capacitors and the area around the ground screw. Under the two electrolytic capacitors, the damage was extensive as to burn the epoxy resin whereby only the free-flowing fiberglass mesh and copper were left. This was the primary fire area.

Within this area, several components were missing and destroyed by the fire. All the components in this region of the board were surface mount. The epoxy resin was consumed by pyrolysis within the PCB layers, which is visible in the picture at the top left. The glass weave was left floating, partially disintegrated, and interlaced by the copper foil. Much of the remaining resin from the PCB had turned black due to the anaerobic burning. This section of the PCB had to stiffen with resin before cross-section could take place. A cross section of the PCB is pictured at the top right.

The failure occurred because the PCB had a void under the electrolytic capacitors. This void coupled with the reduced electrical capacity of the two top and bottom copper layers caused excessive heat; this caused expansion, component movement, MLCC to crack and short. The heat was initially confined to the internal board. The excessive internal heat further contributed to more delamination and copper distortion and movement.

Failure analysis performed by Gideon Analytical Laboratories can reveal candid and accurate results stemming from problems in production or in field applications. This knowledge can be invaluable to a variety of companies in the electronics industry. Product liability is of great concern in today’s market with potential lawsuits lurking; companies are able to save themselves from potential lawsuits by failure analysis and design changes.