How NOT to Solder Headers on a Board

There are two basic strategies in teaching:

  1. Teach and show how things should be done.
  2. Teach and show how things should NOT be done.

I usually do the first method. But there is a lot of value in the second method too!

When I asked all student groups to solder the headers on the Freescale FRDM-KL25Z board, I received one report that the board does not work any more. A quick inspection of the board showed this:

Soldering the FRDM Board Headers

How NOT to Solder the FRDM Board Headers

Wow! Well, I did not plan to use didactic method number two for that teaching material, and I did not plan to teach how to use the soldering iron with solder. But this was enough for me to reconsider my strategy:

Soldering detail

Soldering detail

Not everyone is mastering the soldering iron, and there is first time for everyone. But this piece actually was fascinating. Some details are a special piece of amazing art:

Solder and Header Details

Solder and Header Details

Solder formed balls around the pins, and in some cases even not touching the pads, creating nice connections with other balls: I think if I would want to create something like this, I would not be able to do so:

Solder Balls

Solder Balls

Outcome: That team received a new board :-). In return I asked that I can keep their original masterpiece for my didactics collection under number 2.

They received a big smile, and introduction and hands-on about how to solder the pins correctly:

  1. Heat up the pin/pad for about one second with the soldering iron.
  2. Quickly apply solder.
  3. Keep heating while removing the solder wire.
  4. And then remove the iron.

Now that board looked technically correct and functional, but somewhat boring ;-).

I have learned something too: do not assume that every engineer knows how to solder pins. And that the number of engineers who *know* how to solder just has increased the other day :-).

Happy Soldering πŸ™‚


28 thoughts on “How NOT to Solder Headers on a Board

  1. Looks like they used solder without flux….

    But: it’s very important to make sure these software engineers have some hardware skills. Soldering, what a dry joint looks like, stripping wires, crimping connectors, what to do with heatshrink tube, how to use an oscilloscope (always ground the earth clip!). Plus the invaluable fact that burning skin smells like mushrooms.

    Liked by 2 people

    • That solder has flux. And yes, I agree with you: everyone needs to have some hardware skills, same for everyone needs some software skills. And not using a proper base for any measurement device (logic analyzer, oscilloscope, …) is a common mistake too. But the mushroom thing is new to me, to me it always smelled like BBQ πŸ™‚


  2. Because of your location I presume you are using lead free solder, big change from the old days. Just think the old NASA soldering class was 100hours long, been there and did that.


  3. My tip for new engineers/students soldering thru-hole components is to never directly touch the solder to the tip of the soldering iron. They often want to try to melt the solder with the tip and somehow transfer it to the place they want soldered. :-). As you commented, the solder should have to flow across the joint to reach the iron.

    We have a couple of soldering irons which heat up the tip in under 8 seconds (pace HW100). I would highly recommend the equivalent for business use, although at home I have a very simple iron.

    For surface mount, a mini-wave tip on the soldering iron works very well once you get the hang of it ( This works very well for parts with actual pins jutting out from them (SOIC/TSOP/TSSOP/QFP/etc). For lead-less parts such as QFN, it is more challenging to use.

    For mounting (or remounting) BGA components individually, we often use single use stencils :

    My 2 cents!


  4. Oh well, still, even though that can be considered ‘pretty’, you wonder about common sense…
    Paying so little attention to something so visual, physical and material does not bide well for more abstract matters that you find in software.
    How do you teach what ‘nice’ code is when un-nice (although pretty) connections don’t seem to bother?
    Live and learn….


  5. As others noted, heat the joint and press the solder into the pad/pin. Which increases the tip life as well.

    Some more great pictures, Erich.


  6. I was an electronics failure analyst for many years, and can attest to the fact that in some cases, failure CAN be a thing of beauty – especially under a microscope.


  7. hahaha! This is the scariest solder work I have ever seen! And I just come from “swapping” two pins on the KL25 with 0.5mm pitch this morning… Thanks for bringing a smile to my face also… πŸ˜€


  8. What a lot of great comments and suggestions!

    Erich, may I humbly suggest that from now on you require all of your students to study this web page and then quiz them on proper soldering techniques during the first week of class? Perhaps including pictures of various quality soldering connections for them to rate from good to bad would be helpful.

    EVERY ENGINEER who ever has anything to do with electronics needs to know the difference between a good looking solder joint and anything less, even if he/she does not pick up a soldering iron.

    Where I work we sell multi-thousand dollar machines, some of them with tens of thousands of hand soldered connections. IF ONLY ONE OF THOSE CONNECTIONS FAIL, THE ENTIRE DEVICE IS USELESS UNTIL REPAIRED.

    This can cause lots of problems for the doctors around the world who use our products. One cold solder joint can result in in significant frustration for both the customer and our service department as various modules are shipped back and forth from Europe, Japan, and Mediapolis Iowa, until the intermittantly malfunctioning part is finally identified and replaced. Imagine how much more frustrating it can be when there are two or more cold solder joints in the same machine.

    Engineers need to be highly aware of this part of the industry in order to be better prepared for their jobs.


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