We haave a captive double sided plated-thru-hole shop for in-house products.
 The finished raw boards before component insertion are Copper with Nickle
plating (not HALS) and selective solder mask.  For certain mechanical
considerations with the interface of the PWBs to other non-conductive parts
(plastic housings) of the finished products, we do not wish to have solder
bumps on the back of the finished board at via interfaces after wave
soldering that side (the actual electronics are on top).  Simple solder mask
seems to prevent these bumps from being formed.  Is there an IPC
recommenddaation about soldermasking over thru-hole vias?  The hole may or
may not be closed by the mask.