The ideal thickness is to be thick enough for good solderability, yet thin (flat) enough for part placement. Because of the HASL process and surface tension of solder, smaller pads will have a greater amount of solder as compared to larger pads.
Due to this and coupled with lead free HASL having an inter-metallic two times that of leaded HASL a minimum thickness is more crucial in the lead free process than the tin/lead process.
It is difficult to spec in a certain thickness because of the process so we (Florida Cirtech) concentrate on a minimum thickness and not on a range. Our recommended minimum thickness would be 100 microinches as this should insure good solderability.
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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