Category:PCB PCB Industry Information

Group Administrators: 1 | Group Member: 148 | Group Threads: 374

This Group provides continually the latest information on the most recent trends, forecasts and analysis in the printed circuit board space.

Thread Reply
Marginally Documented Pad Shorts to Maskless PCB Reply 2017-02-15 04:58:38
402 views
2 comments
39 likes

filippo.lalli

Leave A Message

Follow

[Erich Styger] was bit by a nasty gotcha when soldering a QFN surface mount chip. The problem rears its ugly head when combining a chip possessing a padless conductor and a PCB without a solder mask. As you can see in the image above, there is a conductor exiting the side of the plastic QFN, but there is no pad associated with it. For this reason, you won’t see the conductor documented in the datasheet as a pin. It is documented in the mechanical drawing of the package, without any explicit reference to its existence. This is the Jason Bourne of package quirks.
The PCB layout just happens to have a trace exiting right under this conductor. The two aren’t touching, but without solder mask, a bit of melted metal was able to mind the gap and connect the two conductors. [Eric] notes that although the non-pad isn’t documented, it’s easy to prove that it is connected to ground and was effectively pulling down the signal on that trace.
In a recent article on Hackaday I talked about “dangling pointers” and the challenge when interrupts expose the bug. [Erich’s] covered a ton of posts about embedded software. I was doing some poking around and was delighted to find that he covered the same concept and a solution for it using a program calledcppcheck.
39 likes
Statement: This post is only the personal view of the author and does not represent the opinions of ALLPCB.com.

Gabe

Leave A Message

Follow

Please keep doing your great job.

Bernie

Leave A Message

Follow

I must say you have very interesting posts here.
ThreadReply