I'm sending a board for assembly with a through-hole DIP-8 package with a standard horizontal lead spacing of 7.62mm. However, at their ends the pins are wide with a pin spacing of ~8.47mm. Should I modify my footprint to accommodate this wider width or leave the footprint at its default width of 7.62mm? I'm not sure how the fab assembles the DIP packages.
Use the standard DIP footprint with 0.300" (7.62mm) spacing. The PCBA house will compress the DIP to fit. Holes around 0.8mm.
When I assemble a few by hand, I just push the side of DIP against the ESD mat, one side after the other, to roughly get the leads the right distance. Assembly machines pick the DIP package up by the outside of the leads from the tube and compress the leads to the right spacing. Hand production assembly lines probably use tools to space the leads.
In any case, you should use the standard spacing on your PCB footprint.
No changes are required. DIPS are spread to allow straightening either manually or in auto-insertion machines.
Here’s one clever tool that keeps the IC’s in their ESD protected tube.
tl, dr: Use the PCB lead spacing that is specified for the package in the datasheet. For an 8-DIP this will be 0.300" (7.62mm).
Why the weird lead shape, then? The leads are purposely splayed that way to hold the IC in place during wave or hand soldering.
During automated assembly, the auto-insertion machine puts just enough side pressure on the leads to get the pins into the holes. Once the IC is inserted, the machine releases the pressure and the leads spring back. This holds the IC in place.
For hand insertion you can mimic this process using a tool like this: https://www.jensentools.com/jonard-tools-mos-2428-dip-insertion-tool-for-24-to-28-pin-wide-chips/p/606wi753 It does the same thing as the insertion machine: puts pressure on the leads so that you can get them in the board, then releases them so that the IC stays in place.
That said, for prototypes most folks just bend the leads straight to get them into the board and tack the IC in with solder to keep it from falling out when you flip the board over. Lay the IC on its side and bend the leads straight.
You need to modify your footprint to accommodate the actual package and pin dimensions. The fab house, depending on how good they are, will either 1) tell that there's a problem with the hole pattern, or 2) just try to force the pins, by bending them slightly, into the holes.
You may be able to get by with the latter, particularly if this is a one-off or hobbyist project. But I would not recommend that for any type of production run.
I thought the pins were spaced differently along the long axis of the package. But now I see that the spacing being talked about is across the package (pin 1 to pin 14 in a 14-pin DIP). Like others have said, there is fair amount of tolerance in this axis as the pins have a good deal of compliance in this direction. So you should be OK with your standard footprint.