Many broadcom wireless cards are unfortunately unsupported in OpenBSD. There are, however, exceptions, that will work, and that can be installed in Intel Macbooks.

The Wi-Fi card that is generally very well supported by OpenBSD's bwfm driver is the BCM943602CS. This is a full-mac “Airport card” using the BCM43602 chipset, and it has both Bluetooth and WiFi connectivity. (Obviously no Bluetooth on OpenBSD since 5.5.) You can read its technical sheet here.

Theoretically, any model that has a MiniPCIE WiFi card should work. The below are reported on data sheets etc to work.

• Macbook Air:
  • MacBook Air (11-inch, Late 2010, Mid 2011) A1369 - https://support.apple.com/en-gb/docs/mac/133336
  • MacBook Air (11-inch, Early 2014) A1465 - https://support.apple.com/en-us/112032
  • MacBook Air (13-inch, Early 2014) A1466 - https://support.apple.com/en-us/111942

• MacBook Pro
  • MacBook Pro (Retina, 13-inch, Late 2013) A1425 - https://support.apple.com/en-gb/111946
  • MacBook Pro (Retina, 13-inch, Early 2014) A1502 - https://support.apple.com/en-us/111942
  • MacBook Pro (Retina, 15-inch, Early 2014) A1398 - https://support.apple.com/en-us/111935

• iMac
  • iMac (21.5-inch, Late 2013) A1418 - https://support.apple.com/en-us/111967
  • iMac (27-inch, Late 2013) A1419 - https://support.apple.com/en-us/111970

• Further models are likely compatible using a 12+6-30pin Molex Adaptor
• There are ways to install this chipset in certain iMac models as well.

This was tested on the A1502 Macbook Pro and the A1465 Macbook Air. They are good test cases as there are some key differences. The A1465 uses a 2-antenna setup so the 3 UART connectors pose a question and the original Wi-Fi card is also shorter. The A1502 is much closer in all sorts of ways.

1. Follow the iFixit instructions for your model on disassembly. This usually involves getting out your specialised pentalobe and hexalobe screwdrivers and undoing the bottom case screws.
2. Once open, unscrew the retaining screw for the WiFi card
3. With a spudger or some ESD safe tweezers gently disconnect the antenna connectors
4. Remove the original WiFi card by gently pulling and slightly lifting
5. Because the BCM943602CS is longer than the original BCM94360CS2, it will overhang a bit but this isn't a problem. Just make sure you insulate the card from accidental contact with other parts, by either simply wrapping it in electric tape, or using a piece of cut shrink tubing, or anything that will insulate it really
6. Plug in board, plug in the longer antenna connector into J0 (leftmost) and the shorter antenna connector into J1 (rightmost), as pictured
7. Close it all back up
8. Run # fw_update and install the bwfm drivers if you did not yet have them
9. Configure /etc/hostname.bwfm0 as per the manual for hostname.if(5)
10. Rejoice, run # sh /etc/netstart if needed

This is basically a like-for-like swap. Follow your iFixit instructions for opening up your machine, unscrew the bottom case, unscrew the wifi card retainer screw, gently lift the card, bearing in mind that sometimes it is held in place with some putty, disconnect the antenna cables, connect them back in the same order.

On some models (such as the A1465 Air) Internet Rescue over wifi will only work with the original wifi card reinstalled. You can still use Ethernet (with a Thunderbolt dongle) or a flash drive installer if you need to reinstall MacOS.

THX to @morgant@mastodon.social for initial instructions and guidance on making this work.