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.