COMPARISON OF VARIOUS METROLOGIES TO MEASURE VOIDS IN X-RAY IMAGES OF HIGH DENSITY BGA PACKAGE SOLDER BALLS
Authors: Ife Hsu and Raiyo Aspandiar, Ph.D. Company: Intel Corporation Date Published: 5/19/2011
Abstract: As specified in J-STD-001E and IPC-A-610E, the maximum acceptance level of Voids in BGA Solder Joints is set as 25% of the area the void occupies with respect to the solder joint, as measured in the X-ray Image. When there is an excursion beyond the 25% void area limit for BGA solder joints, board assemblers, such as ODMs, typically inspect the balls attached to the BGA component prior to surface mount assembly on board and check for the %void area levels in these BGA balls. Though there are guidelines in IPC-7095B for the acceptable level of voids within BGA balls, there is no specification for pre-SMT soldered BGA balls corresponding to the 25% post SMT BGA solder joint specification. Moreover, the metrology tools used to obtain X-ray images to measure voids in BGA solder balls and joints differ from one manufacturing site to another and introduce variability in the void area measurement between the BGA component supplier and the BGA component board assembler. The JEDEC 14-1 Committee therefore commissioned a Solder voids Task Group to investigate various metrology tools for matching when measuring voids in BGA balls that are attached to the package substrate, priori to soldering the component to the board. This paper will present the results from a couple of round robin studies conducted using 8 different metrology tools, both manual and automated, for measuring the void area within the in X-ray images of high density FCBGA component balls, obtained with a 2D Transmission X-ray tool. These results will also be compared with the void areas measured using a 3D Computer Tomography X-ray tool. This 3D tool is the designated `golden` metrology in this investigation since it is capable of clearly capturing and accurately measuring even small voids in the BGA balls. The pros and cons of the presently used X-ray metrologies, such as 2D Transmission X-ray, X-ray Laminography, and cross-sectioning, and will be also be described.