BGA inner hairline crack

Hallo all, when I remove one from us malfunction BGAs from PCB I saw under X-ray inspection inner hairline crack.(see fig.1.) BGA was dried according to J-STD 033 and reflowed in lead process. When I look at new (baked BGA) under X-Ray inspection I see the same crack line at the same position.(see fig.2.) Have somebody here any experience with this one?

Thanks

Radek

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