Almost Fail of The Week: Doing Surface Mount Reflow Wrong In Every Possible Way and Still Succeeding

Sometimes the best way to learn is from the success of others. Sometimes failure is the best teacher. In this case we are learning from [Tim Trzepacz]’s successive failures in his attempt to solder one board to another using a reflow oven. They somehow cancelled each other out, and he ended up with a working board. For those of you who have used a reflow oven, there will be eye rolling.

[Tim]’s first mistake was to use regular solder instead of paste. We can see how he got there logically; if you hand solder an SMD you melt solder onto the pads first to make it easier. However, the result was that he had two boards that wouldn’t sit flat on each other thanks to the globs of solder on the pads.

Not to be deterred, he laid the boards on top of each other and warmed up the oven to a toasty 650 degrees. Well, not quite. The dang oven didn’t turn to eleven, so he figured 500 would probably work too. Missing the hint entirely, he let his board bake in a nearly 1000F oven until he noticed some smoke which, he intuitively knew, definitely shouldn’t be happening.

The board was blackening, the solder mask was literally bubbling off the substrate, people were coming over to see the show, and he decided success was still possible. He clamped the heated boards together with a binder clip until they cooled. Someone gave him a lesson on reflow, presumably listened to through reddening ears.

Ashamed and defeated, he went home. However, there was a question in his mind. Sure it looks bad, but is it possible that the board actually works? After a quick test, the answer was yes. It loaded some code and an time later he was happily hacking away. Go figure.

34 thoughts on “Almost Fail of The Week: Doing Surface Mount Reflow Wrong In Every Possible Way and Still Succeeding

  1. After a quick test, the answer was yes. “After a test only due to the unforgivable sin of never trying, success was gloriously revealed!” More pop. Booo! /me throws popcorn. “We want Brian! We want Brian!”

  2. Read the article fully before writing your own. He very clearly states a number of times that it was a hot air rework station, not an oven. This can be confirmed by the localized burning that’s exceedingly evident in the photo you chose to post.

    Always nice to hear about some beginner’s luck though.

    1. this is like detailing a car– if you tend to learn your own techniques like i did, everything i do is wrong-wrong-wrong to people that have been swapping tricks since cars started needing to be detailed.

      it’s hard for a lot of people to acknowledge that not everyone does things the same way they do things, and then those same people throw fits when everyone gets the same final result.

    1. The temperature, with a reflow temp/time curve is often included in the datasheets of SMD components. But I think it’s only for solder paste.
      In my experience lead solder can melt at 270°C, but personnaly I solder at 310°C because it is faster.

      1. That sounds about right for the reading on my iron. I do use slightly higher temperatures and a bigger tip for desoldering though hole stuff.

        I did also buy a roll of lead free solder and it splattered and carried on and I have never used except for that brief moment.

        I am still curious as to what may be the correct temperature range for lead free solder on a roll? or even if people use that at all?

        1. No idea about temperatures, but I do use lead-free and I’ve noticed recently that the (soldering iron) bits -and- completely new temperature controlled irons just fail completely to tin (wet) with lead-free.
          Is it just me, or is the industry dumping their pre-RoHS kit onto the hobby market?

    1. Don’t know Tim’s story, but I’m an engineering student and they generally keep us away from anything surface mount for most of our time at uni. The closest we get is using through hole parts with some SMT chips on breakout boards. So, not surprising that not everyone with a degree knows how to reflow.

    2. Well I don’t know if I would use tin/lead solder with a heat gun … but the major part of this problem was assuming the temperature controller was graduated in Fahrenheit and that is probably a mistake that many Americans could easily make weather they have a degree or not.

    3. I got my degree in 1991. According to Wikipedia, surface mount didn’t become widespread until the “late 1980’s”, I know I didn’t start seeing it until long after that. I’m not sure we actually did any soldering at all in college, building our test circuits on breadboards.
      As for clues about surface mount stuff, I had plenty of them! What I lacked were facts…

  3. This article is completely inaccurate. It would be in the best interest of everyone here if it was corrected or simply pulled. A reflow oven wasn’t used at all.

    “The dang oven didn’t turn to eleven, so he figured 500 would probably work too.”–this statement is completely made up. Where did the author get this from? HaD, for the love of hacking, please ensure your writers RTFA.

    1. It’s only partly made up, the part that it was an oven, but he does say “Knowing that I needed to melt solder at 650 degrees Fahrenheit, I turned up the temperature as high as it would go, 500 degrees”

      And the use of ’11’ is of course not to be taken literally, it’s a universal thing that settings go to 10, and that 11 is one above max, so it’s more a saying. It’s like using the term 110%, which does not exist but people indicate something with it.

  4. Just asking: Would it be possible to reflow small PCB with a hot air station (like these cheap chinese things you can get on ebay) instead of an oven? Anybody tried? I mean apply solder paste, place components but then use hot air instead of an oven.

    1. Sorry, i forgot about this. Thank you for your answers, i will have a look at this. The bad thing with hot air reflow is that you can’t really follow the temperature profiles and it’s more difficult to heat the board evenly, but for occasionnel small stuff like breakout-boards it might be an alternative to a bulky oven. A hot air station is more universal.

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