SMTA International Conference Proceedings

2D/3D X-Ray Inspection: Process Control And Developmet Tool

Authors: Zhen (Jane) Feng, Ph. D., Tho Vu, Michael Xie, David A. Geiger, Murad Kurwa; Zohair Mehkri; and Evstatin Krastev, Ph. D.
Company: FLEXTRONICS International Inc., Santa Clara University, and Nordson DAGE
Date Published: 10/13/2013   Conference: SMTA International

Abstract: With more and more BGA and PoP packages used on contemporary PCB boards, achieving the best possible BGA, and PoP solder joint quality becomes extremely important for the PCBA manufacturer. Most of the solder joints of these types of devices are invisible by optical means, thus AXI (Automated X-ray Inspection) is becoming more frequently used on the SMT lines. However, based on our experience, it is very challenging for current AXI machines to achieve defect escape rate of better than 2%, and false call PPM less than 2000 for BGAs, PoP s and some critical packages. Naturally we ask the following questions: What are the best ways to utilize the X-ray inspections techniques currently available? How to optimize the AXI algorithms settings? What is the correlation between AXI and 2D/3D CT X-ray inspection results?

Within this project we focus on two main subjects: 1. Use 2D/3D X-ray inspection to identify solder joint Head-In-Pillow (HIP) defects in BGA devices, and utilize the collected data to improve our AXI programming process. 2. Use 2D/3D X-ray inspection for identifying solder’s joint quality for PoP on cavity board, and improve our SMT process. The 3D X-ray test method used is 3D X-ray Board Level Computer Tomography (Limited Angle Computer Tomography or PCT). All of the above X-Ray inspection methods are completely non-destructive, thus the expensive board does not need to be destroyed during the inspection process.

We analyzed data from four different AXI machines at four Flextronics sites using boards known to have HIP (Head-In-Pillow) defects1. Initially all HIP pins were identified using 2D X-Ray inspection. Recently we used 3D X-ray Large Board CT (or PCT) to produce 3D X-Ray models and images of the areas of interest on the PCB, in order to check and confirm the 2D X-ray results, and would like to see current AXI can detect what kind of HIP type. We used the 2D/3D CT data to monitor the level of success for current AXI machines in finding various types of HIP defects.

As part of our new product development process, we use 2D and 3D large board CT X-ray inspection to identify solder joint defects of PoP packages mounted within a cavity on the PCB. The two X-ray techniques working in tandem let us determine precisely the type and the location of the defects, thus providing extremely useful data during the SMT development process. We will also report the improvement data for the novel cavity PoP process and discuss our process development methodology.

Key Words: 

AXI, HIP, PoP, 2DX, 3DX, CT.

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