I would say that we don't know whether they are a long term reliability issue if exposed to harsh environment applications. The shrinkage cavities are formed in SAC alloys such as SAC305 in part due to the alloy not being a eutectic.
SAC305 has a mushy zone thus the differences in solidification behavior. I do not know of any lab results or test data that proves a shrinkage crack will never cause a failure under severe conditions.
There is some evidence that a cavity in the maximum shear plane can initiate a crack under vibration conditions (Blattau, SMTAI Conference 2005). Others tests have shown a shrinkage cavity to expand within a 1000 cycles under thermal cycling conditions of -40 to +125°C.
These tests show that under certain conditions, shrinkage cavities may be a reliability concern but do not prove that a shrinkage cavity will always cause a failure. Shrinkage cavities are a concern thus the guidelines on the depth and contact with the lead or land stated in IPC-610-D.
You might want to look at some of the other lead free alloys that don't have this issue, i.e. SN100c.
Mike Scimeca
President
FCT Assembly
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.
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