Tape-Peel Testing as a Simple Method to Evaluate the Adhesion of Coated Layers on Metal Core PCB

Abstract

Conventional printed circuit boards (PCBs) may be replaced by thinner metal-core boards for some applications, as well as for package substrates. Using thin, metal-core technology may provide advantages for radio frequency (RF) circuits and packages, and increase heat dissipation for high power applications. The metal-core technology discussed in this paper has several layers including the metal core, electro-coated dielectric, sputtered metal layers, and electroplated copper. For PCB and substrate reliability, it is important to have sufficient adhesion between the dielectric layer and plated copper. Sputtered metal layers with cleaning pre-treatments are one of the methods to improve the interfacial adhesion. This paper describes an efficient testing method for the adhesion of a thin sputtered metal layer to a dielectric substrate. In this method, adhesive tape was attached to the surface and peeled off at 90 degrees in a tensile tester. Due to the sub-micron thickness of the sputtered layers, conventional peel test methods could not be applied. Typical adhesion testing of upper layers like paint coatings use a lattice pattern. The new method provided a convenient, repeatable way to evaluate the adhesion of three different sputtered metals with fifteen different pretreatment combinations. The test results were used to choose the sputtered metal and were later confirmed by testing the copper plated assembly using the metal adhesion specification in the industry standard IPC-TM-650. A review of other methods and the need to identify an easy to use method which can provide repeatable quantitative measurements.