Authored By:
KH Ooi, Ivan Khaw, Zhen (Jane) Feng, Ph. D., David Geiger, Murad Kurwa
FLEXTRONICS International Inc., Guangdong, China
Summary
Bottom Termination surface mount Components (BTC) are extremely popular because of their low cost, low stand-off height and excellent thermal and electrical properties. In this manufacturing arena, more and more connectors are utilizing the printed circuit board (PCB), due to its ability to allow convenient memory expansion in servers and embedded applications in communications. The challenge for the industry is to achieve the best possible BTC and connector solder joint quality.
The following questions are keys to our discussion: What is the best way to use test and inspection techniques? How does one obtain accurate AXI (Automated X-ray Inspection) data and images for surface mount technology (SMT) process improvement? How does one minimize voiding in thermal pads caused by changing design rules in order to meet stringent customer requirements? How does one reduce the use of mechanical cross-sectioning, since it destroys costly PCBs and is time-consuming?
Identifying product defects associated with the manufacturing process is a critical part of electronics manufacturing. When faced with the need for high yields, especially for new product introduction (NPI), AXI faces challenges with new packages and processes, such as BTC and connectors. In this project, we will focus on how to use AXI to identify BTC and connectors, especially for voids from AXI testing of Mosfet and PQFN packages. The test methods include AXI, 2DX and cross-section. We would like to reduce destructive methods in order to have a high-accuracy, low-void percentage from DOE (Design of Experiments).
We analyzed data from Tomosynthesis of AXI3 machine, AXI4 machine and 2DX, cross-section (virtual and horizontal cross-sectioning) using QFN package types (Mosfet and PQFN). The goal is to look for a correlation between AXI and 2DX, 2DX and cross-section for improving accuracy levels with AXI data. The SMT process was improved, with good feedback of X-ray data and correlation results.
Conclusions
The following are conclusions which can be drawn from this work:
Make sure AXI machines are under normal testing conditions, especially for NPI. For accurate calibrations, the AXI machine needs to have its own void standard board.
AXI Gage R&R is important; however accurate AXI testing data is more important for process improvement.
Focus on AXI balance of defects missed percentage and false calls PPM.
Use non-destructive methods to identify process issues, and reduce cross-section samples by first comparing results of the other test methods.
The AXI system is not only a test machine - it is process improvement tool. Using real-time data measurement feedback is the key to the process4. By using AXI as a SMT process improvement tool, we have reaped many benefits. Figures 16-18 list the yield of DIMM connector, QFN, and Q-Mosfet for this project for the last seven months.
Working with vendors can generate better performance in the AXI field. Each X-ray machine has its own strengths and weaknesses. 2DX is an X-ray microscope which is useful as an AXI reference for certain critical components and borderline defective pins.
Initially Published in the IPC Proceedings
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