I am looking for an eagle footprint that can accept both a standard 40 pin DIP socket or a ZIF socket. Alternatively, if you have tried this and found it to be impractical I'd like to hear that too.
update: thanks for the contributions. I had not realised that different brands of ZIF sockets can be very different in pin spacing. The ZIFs I have is marked 3M (although it is more likely a clone). The two rows are definitely not at the standard distance from each other, yet close enough to the standard distance that two holes is out of the question, the holes would overlap which AFAIK is frowned upon by boardhouses. I now made the holes larger, I'll see whether this works out OK (the file was sent to the PCB house today). The holes are now so large that no trace will fit between two pins, but the autorouter did not mind 🙂
update 2: larger holes worked OK. It is a bit of a compromise now, I would never use such large holes for a normal DIP socket, but is still fits OK.
supercat's answer was the most usefull to me, but it is in a comment 🙁 I have one of those black ZIFs too, I like it much better than my '3M clone', but it costed maybe 10 times as much…
Best Answer
The pins of a 40-pin ZIF will have the same spacing as a 40-pin DIP. The issues to watch out for are: (1) some ZIF sockets have pins which require larger holes than would be required for most sockets, and (2) nearly all ZIF sockets are wider or longer than ordinary sockets; many are significantly longer. If you wish to solder a ZIF socket directly into a board, you should leave room for this. My normal preference, however, is to solder an "ordinary" socket into the board and plug a ZIF socket into that. If you take that approach, it may be possible for the ZIF socket to overhang some low-clearance components.