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Editor’s note: This article is based on a paper by the authors initially presented at APEX EXPO 2025. A link to the original paper can be found at the end of this article.
The process of measuring BGA samples for thermal warpage is subject to industry standards from both JEDEC, in JESD22-B112C and JEITA ED7306.1,2 Additionally, these standards establish allowable warpage values based on ball size and ball pitch, for the JEDEC standard, pass/fail further established in JEDEC SPP-024.3 Standard practice in these standards for measuring BGA warpage is to remove the solder balls in order to measure only the substrate surface. However, as both ball size and package thickness decrease, the practicality of removing solder balls without altering the sample shape has become increasingly challenging.
Determining warpage of BGAs can be challenging due to factors like surface preparation, size, or data processing. The solder balls can be physically sheared, which can potentially damage the substrate surface and alter the local surface topology.
Even when the solder is completely removed, light still reflects more brightly off the copper or gold pads beneath it. Applying a coat of white paint maintains consistent surface brightness and mitigates noise due to damage caused by the shearing process. However, ball removal alters the sample composition, potentially affecting warpage and thermal mass.
Alternatively, paint can be applied to the surface while the solder balls are still intact. Post processing requires digitally selecting a region of pixels that encompasses the solder ball and scanning the entire image looking for matching areas. Processing time is dependent on the number of pixels for both the solder ball region and the full image. Searching for a 14 x 14 pixel area in a 750 x 750 image will take a greater amount of time than searching for a 14 x 14 pixel area in a 500 x 500 image. Solder balls must be removed from all acquisitions taken throughout the thermal profile. This can be accomplished either by repeating the previously described process for each individual image or by masking multiple images using the ball location from a single reference image. As samples expand, contract, or shift during the thermal profile, the masked regions may become misaligned. Careful attention is required to ensure the correct areas are masked for each temperature.
The methods presented in this article eliminate the need for solder ball shearing and painting. However, the primary advantage to these methods is the simplified data processing and time savings associated with it.
To continue reading this article, which originallly appeared in the October 2026 SMT007 Magazine, click here.
