PCB Barrel Cracking
What is it?
Barrel cracking is a stress related problem that occurs in printed circuit boards that contain plated through holes which interconnect the conductive layers of the board.
Why does it happen?
It is caused as a result of thermal coefficient of expansion mismatches between the copper conductors and the PCB dielectric material. During any thermal changes such as occur during soldering, these thermal expansion mismatches cause a build up in stress which can, in severe cases, damage the copper barrels in the plated holes.
Barrel cracking has been known for some time but as boards have become thicker with smaller diameter holes, hole aspect ratios there has been a related increase in its occurrence. Higher soldering temperatures needed for Lead-Free assembly will potentially lead to even greater stresses being put on the barrels and an even greater chance of barrel cracking occurring.
What problems can it cause?
Barrel cracking can cause a failure in the electrical connections of plated through holes which can be difficult to detect. They may appear as intermittent faults with the crack opening up as the board expands when exposed to higher temperatures and closing when it is cool.
How can it be prevented?
The key to avoiding this problem lies in the quality of the PCBs. The manufacturing process and specifically the hole metallisation process is very important. The incidence of barrel cracking can be reduced by the use of an optimised hole wall (desmear process) and a good quality metallisation process that gives a uniform plating thickness through the holes. |
