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Topic: Contact holes ruined - bad quality or my fault?  (Read 642 times) previous topic - next topic

Edgar1

Many shields come with square pins. Recently I de-soldered a couple of them.
For most shields this worked fine. After the pins were gone I had clean holes with good contact to the traces.

But with two SD-Card shields I ruined the holes and the connection to the traces. On one of them only one trace connection was gone and I fixed it with a little wire. On the other module several traces are ruined and probably I won't spend the time trying to fix it soldering to micro SMD parts.

My question is: Should these holes easily survive soldering and de-soldering a couple of times?
Are there big quality differences between the PCBs?
Or did I likely do a bad de-soldering job and that ruined them?

Normally my soldering skills are relative good and I have a temperature controlled Hakko soldering iron.
But I do a lot more soldering than de-soldering, so maybe I just have to learn this.

What is your experience especially with removing square pins with lots of contacts from shields?

MrMark

It's pretty easy to desolder/remove single pins.  It is much more difficult and risky to remove multipin components because one has to melt the solder on all pins simultaneously. 

If there's no need to preserve the component one can clip the leads or otherwise cut it up prior to removal, such that only one pin at a time need be removed.

In addition to a good soldering iron, solder wick and a solder sucker are handy for this sort of thing.

srnet

What is your experience especially with removing square pins with lots of contacts from shields?
It takes a great deal of care, I do it pin by pin, very rare to have a problem. Removing an entire connector in one go is very risky, unless you have one of those solder wave machines. 

I also think it would be unreasonable to expect boards to be built or designed so that they can undergo a few iterations of re-work.

Would consumers be prepared to pay a premium for 'higher quality' boards with thicker copper for instance ?
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wolframore

Excessive heat can destroy traces and pads and eventually the board.  I've done this before...

Bad de-soldering using too much heat because there are so many pins while pulling on the component can damage even the best boards and sometimes the components.  Use a lot of flux and de-soldering braids next time... they make tools for re-work... using a soldering iron to remove mulitple pin type components can be a little like using a blowtorch instead of an oven to cook something.

Its like surgery some of the components are very sensitive to heat and can be damaged along the way.  Work on your technique.
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dougp

I also think it would be unreasonable to expect boards to be built or designed so that they can undergo a few iterations of re-work.
I had to do this recently on a shield from Electronics-Salon to reverse the one-piece terminal blocks.  I anticipated ruining the board with repeated heatings to tediously pull the blocks a little bit at a time but they survived with no apparent damage.

It's important to have a well tinned, sufficiently, but not excessively, hot tip.  Sometimes I even add  solder to facilitate heat transfer to the joint.

Also, if you can get the component out it's OK to leave some solder behind.  It's actually easier for a solder sucker to pull the solder out of the hole without the component lead in there interfering.
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david_2018

I have had boards that the pin was such a tight fit in the hole that even removing a single pin at a time was difficult. Loose tolerances on the connector and the pc board sometimes add up in the worst way.

DrAzzy

Most commonly, damaged traces come from excessive soldering iron temperature. At 700, I almost never lift pads, at 800 it will happen very easily.

Some boards will be more or less sensitive to this depending on how well made they are.
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wolframore

Eek 700F is 370C most components won't last long there. I get nervous at 240. Most solder will melt just fine at 200.
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wolframore

Eek 700F is 370C most components won't last long there. I get nervous at 240. Most solder will melt just fine at 200.
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- this is a mnemonic from BEC

JohnRob

#9
May 25, 2019, 04:45 pm Last Edit: May 25, 2019, 04:54 pm by JohnRob
@wolframore

Quote
370C most components won't last long there. I get nervous at 240. Most solder will melt just fine at 200
At 240 °C you will have to hold your iron on a joint much longer than you should.

With the iron I have I can select tips that match the joint size.

I found the best temperature is in the 350 - 370 °C area.  When soldering a joint, the iron is at the joint for maybe 3 seconds.  This is far too short to raise the board material to above the tg.

When I remove a header, I first cut the plastic away leaving each pin independent.**
I then use an iron to remove the pin.
I then clean the solder off using a solder sucker (I use one of the blue plastic ones, seems to work the best for me)

I have been known to use my air compressor nozzle on a stubborn hole, but it makes a mess.


** in my experience you can save the board or the header, not both (at least not consistently)

@Edgar1

Quote
My question is: Should these holes easily survive soldering and de-soldering a couple of times?
Are there big quality differences between the PCBs?
Or did I likely do a bad de-soldering job and that ruined them?
I would not expect the holes to survive multiple desoldering operations, especially if the traces to the pad are in the small (thin) side.

Boards do vary in quality but the basic materials are mostly the same.  Small pads and fine traces are the most challenging to desolder.


I think you would be better off finding a way to make you connections without removing the pins.  I use Female-Male dupont jumpers.

Please do not PM me with thread based messages.  If your thoughts are worth responding,  the group should benefit from your insight.

wolframore

@JR I wasn't thinking iron. You're right I'm set to about 280 on my iron.
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