X-ray Inspection Methodology on QFN and BGA

Transmission X-ray is one of the X-ray methodology that is applied for Quad Flat No Leads (QFN) solder joint inspection at Surface Mount Technology (SMT) post reflow process in Printed Circuit Board assembly (PCBA) industry. This can be upgraded to Computed Tomography (CT) by adding rotating mechanism to hold the PCBA under inspection. However, the limitation of transmission X-ray methodology on QFN inspection is the qualitative inspection with reference to IPC-A-610x whereby only general inspection criteria provided. Example: from x-ray image we can see the wetting evident however fillet length or thickness is not specified. Without a quantitative inspection methodology on transmission X-ray, this caused problem on verifying and optimizing the SMT process parameters for QFN in order to achieve a high and sustainable PCBA yield in High Volume Manufacturing (HVM). This paper will share the idea of utilizing basic element of X-ray images which is called pixel for QFN solder joint inspection. The invention of quantitative inspection methodology in transmission X-ray Vs conventional transmission X-ray have successfully eliminated “vague” judgment on QFN inspection in PCBA industry. In addition, this paper will discuss and share the prelim result on Ball Grid Array (BGA) inspection to address head-in-Pillow (HiP) solder joint defect detection.