17
\$\begingroup\$

I have found a hardware bug on a board design after many PCBs have been manufactured but not populated. I can fix the problem by removing a SOT-23 component and putting a wire across two of the pads.

I have too many PCBs manufactured that manually installing a wire across the two pads of the removed component is not economical in time or money.

How can this be fixed using an automated production method? Are there components available to fix this kind of problem, i.e. a package with just a wire between the two pins?

The link in question is one of the SOT23-5 diagonals.

One suggestion is to use a zero ohm resistor. These typically come in rectangular packages with rectangular leads.

Would a pick-and-place machine handle resistors placed at 45 degrees to the pads?

What would happen during reflow? Would the surface tension due to the incorrect alignment of the leads to pads cause the resistor to spin and detach from the intended pad?

\$\endgroup\$
1
  • 6
    \$\begingroup\$ How about putting a zero ohm resistor? \$\endgroup\$
    – Whiskeyjack
    Commented Jan 18, 2016 at 10:51

3 Answers 3

Reset to default
36
\$\begingroup\$

You can buy zero Ohm links in a SOT23 package. Various connections are available, have a look at http://www.topline.tv/SOT_jumper.html

\$\endgroup\$
5
  • 3
    \$\begingroup\$ That's amazing there is enough of a market to support so many different types. Never knew about these -- will keep them in mind for configuration jumpers. \$\endgroup\$
    – tcrosley
    Commented Jan 18, 2016 at 11:17
  • 1
    \$\begingroup\$ @tcrosley evidently a lot of designers make mistakes :-). I had to find these for a friend... \$\endgroup\$
    – Steve G
    Commented Jan 18, 2016 at 11:25
  • \$\begingroup\$ This is exactly the kind of device I was after. Unfortunately they do not do a link for the offending device (see edited question text). \$\endgroup\$
    – Iain Rist
    Commented Jan 18, 2016 at 13:16
  • 1
    \$\begingroup\$ I tell a lie. I have found the one I would need. \$\endgroup\$
    – Iain Rist
    Commented Jan 18, 2016 at 13:24
  • \$\begingroup\$ You can fit a SOT 343 or SOT 143 instead. Take into account that these devices are not so common and might cost you more than hand assembly. \$\endgroup\$
    – Lior Bilia
    Commented Jan 18, 2016 at 13:33
7
\$\begingroup\$

I've used a 0805 jumper for this exact purpose before. Angle is pretty arbitrary to a pick and place. It may take a little longer to place a component on a 45 than a right angle, but it can do it. During reflow, it's not much different than if it were a normal set of 0805 pads, the jumper will center up between them. It's not ideal for mass production, but it will work to get you through to a revision.

\$\endgroup\$
2
  • \$\begingroup\$ I think the issue may be that the resistor would bridge multiple pads because of the angle. \$\endgroup\$
    – Passerby
    Commented Jan 18, 2016 at 17:33
  • \$\begingroup\$ @Passerby The board would have to be pretty dense for that to be an issue. \$\endgroup\$
    – Matt Young
    Commented Jan 18, 2016 at 17:56
6
\$\begingroup\$

As an alternative to the better answer of a sot-23 zero-ohm link, depending on your needs, a sot-23 diode package or array may be better. It would maintain a reverse bias blocking effect like a regulator should. Different configurations exist, in single and dual or quad.

enter image description here

\$\endgroup\$

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