With a significant amount of pressure, exerted by the nails under BGAs, there is a high risk of breaking the solder joints, Hence, it is crucial to avoid placing a test point under a BGA component. At least, leave a 5.08 mm (200 mil) gap on the four sides of the BGA to allow placement of the upper contrast with a 3 mm diameter. This clearance is common if two BGAs are placed side by side. Read more here.
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