9
\$\begingroup\$

I was tearing down some old CD drives and while taking a look to the PCB I found two pointy solder spots, connected to the first pin of each side of a chip which makes me think is an EEPROM.

There seems to be no trace connecting to these.

What are they used for ?

Here's a picture :

enter image description here

Other odd shaped pads in the same direction :

enter image description here

\$\endgroup\$

2 Answers 2

Reset to default
13
\$\begingroup\$

These are solder-thieving pads, I think.

This is indeed related to wave soldering process, as @Ignacio had mentioned, but it's not just an indication of travel direction. As the IC travels through the wave, the solder accumulates and it can short the legs towards the end of the IC that enters the wave last. Solder-thieving pads give the excess solder a place to go, which reduces the likelihood that it will build-up and create a short.

Here's a more abstract example (Source)

enter image description here

If these are solder-thieving pads, then every surface-mount IC (at least on that side of the board) should have a pair of odd-shaped pads (all pointing in the same direction).

\$\endgroup\$
3
  • 1
    \$\begingroup\$ This does seem more likely, given both that they are on the bottom of the board and their topology. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Nov 9, 2014 at 5:16
  • \$\begingroup\$ I cannot post a photo in the comment section but, yes it makes sense because there is other odd shaped pads in the same direction which fits your explication \$\endgroup\$
    – GmodCake
    Nov 9, 2014 at 16:22
  • 1
    \$\begingroup\$ @GmodCake: Could you post a photo of the other odd shaped pads by editing your original question and appending that photo to the end? \$\endgroup\$
    – davidcary
    Nov 9, 2014 at 16:58
3
\$\begingroup\$

They are most likely used to provide indication of the direction of travel of the PCB through a wave soldering machine. This is evidenced by the buildup of solder towards the back ends of the arrows (and in fact all exposed metal on the board), with much less towards the points.

\$\endgroup\$
5
  • \$\begingroup\$ Why would they make contact with the pins ? And why just not use silk screening ? \$\endgroup\$
    – GmodCake
    Nov 9, 2014 at 5:04
  • 2
    \$\begingroup\$ Maybe the board designer was in a whimsical mood that morning. It does happen. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Nov 9, 2014 at 5:05
  • \$\begingroup\$ Although to be fair, the silkscreen on that board is fairly difficult to see. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Nov 9, 2014 at 5:06
  • \$\begingroup\$ The silkscreen is only "visible" on the order side, which now make sense, thanks ! \$\endgroup\$
    – GmodCake
    Nov 9, 2014 at 5:08
  • \$\begingroup\$ And look at that fan-shaped thing in the lower left, too! This is an interesting PCB. \$\endgroup\$
    – John Honniball
    Nov 9, 2014 at 10:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.