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Phonoclone boards, soldering, and Q1, Q2.

Posted 7th February 2013 at 06:34 AM by rjm

This is in response to several recent emails I've received, where people were having problems with, typically, one board having a bad V+ or V- regulated voltage output.

The number of cases relative to the number of boards shipped caused me to worry that a manufacturing error might have occurred, so at my request I had a customer return the phonoclone boards he had built to me for inspection.

I'm happy to report that the problem was traced to poor soldering technique, the boards themselves are fine. What had happened was solder had cooled before the component had fully settled, and pushing the component down to the board surface then tore the trace away from the bottom of the board, breaking the circuit.

Subsequently, thinking the transistors blown, he replaced them, doing a fair bit of damage to the pads of Q1, Q2.

Fortunately, I was able to fairly quickly set everything to rights, and the boards are now on their way back to him.

Lessons learned:

1. Soldering these boards is actually fairly difficult. The trace is a thin copper foil, 0.035mm thick, bonded to the fiberglass board. It can come unstuck and rip or tear. It takes practice and good, consistent technique to do it right. A powerful (60-80W), variable temp iron helps!

2. Once things go wrong, things tend to go from bad to worse. The pulling components in and out of the boards, especially without proper de-soldering tools, degrades the pads and traces. If the boards are built with the transistors reversed or switched, or if the board is accidentally powered up with V++ in V-- or some other strange configuration that puts V-- negative wrt COM, chances are you are going to damage or destroy both the electrolytics and some or all of the silicon, basically precluding any real chance of repair.

So, please be careful. Get it right the first time. If things do go wrong, stop and get in touch with me rather than pulling things apart.
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  1. Old Comment
    dimkasta's Avatar
    May I suggest bigger pads? We have talked about it before. Even if you can t easily alter the component toolset, it should be fairly easy to apply plain bigger pads on top of the existing ones.
    Posted 7th February 2013 at 10:01 AM by dimkasta dimkasta is offline
  2. Old Comment
    rjm's Avatar
    This could be done for the resistors, but for the rest of the components the pad size is restricted by the lead pitch. (The larger electrolytic capacitors already come with a healthy pad size. The transistor pads, for example, are pretty much stuck as they are.)

    Home-etched boards seem to be far more robust than the ones I get fabbed. The copper layer has less tendency to delaminate. I could request double-weight copper layers, but last time I did that people complained about the higher thermal conductance: the heat wicked away from the pad area so quickly it was difficult to solder!
    Posted 8th February 2013 at 08:12 AM by rjm rjm is offline

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