Poison via effect in manufacturing

Posted on Wednesday, August 1st, 2012 in PCB Review by DP

From the comments on our earlier DIY BGA soldering teardown post, JesseJ points out the poison via effect that will also break the connection to the BGA.

Image above is from the previous post, depicting the capillarity effect where a via sucks the ball of solder in, and prevents contact to the BGA.

Just as a comment on the ‘other side of the coin’ when manufacturing an IC, vias can present an opposite problem with the same result. If all moisture isn’t ‘baked’ out of the wafer before the vias are processed, it is possible for some moisture to be ‘out-gassed’ at the via site breaking the metal via tube – also resulting in a poor/broken connection. This failure is sometimes called a ‘poison via’ and is the opposite of the capillary action on the PCB via, with the same result. Whooda thunk!

Via the comments.

This entry was posted on Wednesday, August 1st, 2012 at 7:00 pm and is filed under PCB Review. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

One Response to “Poison via effect in manufacturing”

  1. bearmos says:

    On the PCB side of things, here’s an article from a PCB fab that goes over a couple of the via options:
    via tenting, caps, and plugs. This just landed in my inbox this morning – what interesting timing. . .

Leave a Reply

Notify me of followup comments via e-mail. You can also subscribe without commenting.

Recent Comments

  • Drone: So these go for around $330 USD and NO published calibration procedure online or otherwise? Given what's inside - I don't think I'll be considering...
  • Pekka Akselin: This is ridiculous!? :-) We are back at 256(!) byte EPROMs that needed multiple, a handful, of voltages to run! :-(
  • KH: Let's try a back-of-envelope calc balancing energies. From MCP1700 datasheet, there are graphs for a 200mA load step. Estimate the energy shortfall as 12uJ. Say...
  • Daniel: It's been a week and my comment is still awaiting moderation. Apparently the CIA doesn't want their involvement known?
  • KH: Agree, so okay, I guess he must have learned from somewhere. 100nF and 1000uF is so far apart, that was jarring; it's more magic incantation...