Problem with no-clean flux spattering on in-circuit testing pads diagnosed by EDS analysis

• Solving issue in real manufacturing process
• Diagnostic of non-conductive spots on testing pads causing wrong result of in-circuit test
• Determination that the non-conductive spot was a flux residue
• Suggestion of possible solutions for flux spattering reduction: use of suitable solder mask

Surface Mount Technology (SMT) assembly often faces the issue of residues on In Circuit Testing (ICT) pads. These residues may have non-conductive character and therefore in-circuit test may mark tested product as failed though they would have worked normally. Since it is not possible to export such marked products, the total production quality decreases. In this work, we analyze the real manufacturing problem using Energy Dispersive Spectroscopy (EDS) analysis of the stains with the aim to find the possible source of residues that appear on the testing pads during the mass electronic assembly or during Printed Circuit Board (PCB) production. Analysis of potential source of residues together with its diagnostic and confirmation of its source is presented in this work.