線上BGA影像檢測之探討與改進

Abstract

本論文是針對改善一套BGA的影像檢測系統所進行的研究。內容先 解說BGA錫球在基板上植球狀況的缺陷和分類情況，再介紹檢測缺陷所使用的規則。對於檢測流程所需的各個影像處理環節，則經由分析多種方法的應用結果，比較出最好的採行方式，找出了最適合的二值化門檻值以及精度較佳的次像素法，此兩種手法有助於改善原系統的性能。為了提昇系統的檢測速度﹔同時以最小誤差圓法逼近錫球外形，並引入真圓度的定義，防止有形狀缺陷的錫球通過檢測。為了健全系統的功能，也針對檢測取像時BGA基板與CCD之間的角度偏位及補正方式進行了相關的探討和研究﹔並進一步提出具體的改善。此外，本文對於系統的校正也有詳細的介紹，期望能對BGA檢測的實務有所助益。 最後的實驗結果顯示，改進後的系統，除了可對機械定位不良的BGA基板進行正常的檢測外，在尺寸量測的穩定度上也有所提昇。在檢測336顆直徑為0.63mm的BGA產品時，全部花費時間只要0.3秒，大約是原來系統所需時間的四分之一而已。大幅提昇檢測的效率。

The purpose of this thesis is to improve a preliminary developed BGA(Ball Grid Arrays) inspection system. The contents first provide an overview on all kinds of flaws of the BGA devices, then introduce new rules for defect detection. By comparing results of different methods for each image processing steps of inspection procedure, we try to look for more suitable ways. We find out that the most suitable threshold value for image segmentation and a better sub-pixel edge-detect operator would be helpful to upgrade the original system. To improve inspection efficiency, we use least-square error circle fitting method to approximate the shape of solder balls. Moreover, we introduce the definition of circularity to prevent defective solder balls from passing the inspection. To improve the functionality of the original inspection system, we provide an improvement proposal for the compensation method of the moving angle deviation of between the BGA substrate and the CCD camera during the image capture procedure. Finally, the contents have complete introduction for system calibration, which can aid the implementation of the BGA inspection. The final outcomes show that the upgraded system not only successfully inspects BGA devices with no correct position, but also has more stability in size measurements. It takes the upgraded system only 0.3 seconds to complete inspection of a BGA device with 336 solder balls of 0.63mm diameter. This is 4 times faster than the original system.