Choosing the right copper thickness plays an integral role in circuit board assembly. When considering the thickness of your PCB copper, there are two things to keep in mind. The first element to consider is the barrel’s current capacity for heat rise. The second is mechanical strength, which is determined by the thickness of the copper, as well as the size of your plated-through hole (PTH) and the presence or absence of support vias.
Choosing Materials
There are a number of materials that circuit board assembly services can choose from when designing a PCB. Such options include the standard FR4, which operates at a temperature of 130 degrees celsius. High-temperature polyimide is another option — this material can stand up to 250 degrees celsius. If the application you are building will be subjected to harsh or high-temperature environments, a material like polyimide should be considered.
Tests have been made specifically for circuit board assembly services to find the thermal fortitude of a printed circuit board assembly. Thermal strains come from different PCB assemblies and repair processes. During these times, the distinctions between the coefficient of thermal expansion (CTE) and the PCB laminate drive enough power for crack nucleation as well as the growth-to-failure of the circuit. PCB manufacturers use thermal cycle testing (TCT) to check for increases in a circuit’s resistance while it goes through thermal cycling from approximately 25-260 degrees celsius. Increases in resistance are indications of a reduction in electrical integrity. This is often due to cracks in the copper circuit.
Thermal cycle testing results show manufacturers that the rate of failure can become inadmissible, no matter the material of the board. Studies done on standard boards (FR4 with 0.8-1.2mil copper plating) show that after 8 cycles, 32% of circuit boards fail. Boards with more exotic materials can show impressive improvements to this rate of failure—boards with cyanate ester only have a 3% fail rate.
However, these high-end materials are much more expensive and can cost anywhere from 5 to 10 times more than typical materials. Exotic board materials are also much more difficult to process. These factors make them prohibitive, forcing many manufacturers to use more traditional materials.
Making Your Printed Circuit Board Assembly Efficient
Heavy copper circuit boards can actually eliminate most failures completely. In fact, using a 2 ounce-per-square-foot of copper to plate to a hole wall can reduce the rate of failure to almost zero—this means that a thicker copper circuit is essentially impervious to any stresses that thermal cycling subjects it to.
Selecting the right thickness of copper is essential for a successful PCB assembly project. Making the wrong choice can be detrimental to your design, so it’s best that you work with an experienced manufacturer that can provide expert advice on the best methods of assembly. Star Engineering is a full-service contract manufacturer that has ample experience in designing, testing, and manufacturing optimal circuit boards for our clients. Contact Star Engineering today to get started on your circuit board assembly project.
