Printed Circuit Board

A PCB manufacturer approached ASMAC with a PCB plated with a typical immersion gold layer over an underlying nickel layer. The manufacturer reported that some areas of the gold plating surface exhibited a reddish discoloration and inquired whether this could be due to organic contamination.

Printed Circuit Board Analysis

Upon learning that the client suspected the discoloration to be caused by foreign organic contamination on the plating surface, our staff inspected the sample using a stereo microscope. From the enlarged surface image, we observed that the stained region was small, making it impractical to perform solvent extraction for chemical analysis to determine its nature. We therefore suggested to the client that we proceed with Fourier Transform Infrared Microscopy (FTIR) in Attenuated Total Reflection (ATR) mode. This method is a simple and cost-effective way to screen for organic matter, even on tiny surfaces. If organic signals were detected, they could be magnified for further analysis.

After obtaining the client’s approval, we conducted the FTIR analysis. However, the results were negative, indicating no significant organic signals on the gold plating surface.

Having ruled out the possibility of major organic contamination, we recommended that the client investigate the chemical depth profile of the stained region to determine whether trace amounts of organic elements were present and to identify other elemental factors that might be contributing to the issue. To achieve this, we proposed using X-ray Photoelectron Spectroscopy (XPS), which is equipped with an ion sputter gun to remove the plating layer by layer. XPS would allow us to determine the composition and chemical states of the elements of interest in each freshly exposed layer after each sputter cycle. With this compositional and chemical information, we could assess whether the issue was due to corrosion, a black nickel case, or foreign object attachment.

After receiving essential background information from the client, such as the plating layer thickness specifications, we set up an XPS depth profiling analysis procedure. The final results revealed the presence of sulfur within the top 20 nanometers of the gold plating, which should not exist under proper conditions. Additionally, an abnormally high carbon content was observed on the gold surface.

The client concluded that these findings likely explained the discoloration on the gold plating and requested that ASMAC summarize the results in a test report. This report would be shared with their production team for further investigation and follow-up actions.