Group Actions
Engagement
  • Author Author: shabaz
  • Date Created: Date Created
  • Views 8408 views
  • Likes 17 likes
  • Comments 28 comments
Related
Recommended

Drag-soldering Surface-mount components

shabaz

I had to solder an IC today, nothing new there, but usually I'll use a 1mm conventional soldering tip (slice off conical shape) to solder each individual pin one-by-one, deal with any bridges with desoldering braid, and call it a day.

 

There are dozens of different ways to solder though. I have a reflow oven, but it is overkill for a single IC. I have a pre-heater and a hot air tool but the ones I have are under-powered. 

 

Although I have seen an expert present drag soldering once, I have never tried it because I've been ok with the way I do it - it works, although it is a bit tedious. However, there has been a drag-soldering tip (also known as a spoon tip or gull-wing tip) in my drawer for years, of size 1.9mm diameter. I figured I'd give it a shot since I was soldering a relatively cheap component, and with the recent activity on element14 concerning soldering tools Cool Tools Kit Awards 2020  and soldering station reviews Weller Soldering Station WT Series I figured I'd post a photo of the results..

 

The part was PCF85176T which is a 56-pin 0.5mm pitch device - it was for an LCD board Building a 3.5 Digit Low Power LCD Module .

The finest SMD part I've had to do with a soldering iron was 0.4mm pitch, so this was not going to be as bad as that, but still a good test.

 

The result with the drag soldering was quite good! If your soldering iron accepts such a tip, I think it is worth giving it a go!

 

image

 

Here is the result, close-up (click to enlarge further):

image

I didn't take photos or a video [edit - see below for a second attempt which was recorded] of the process (because I fully expected to fail the first time), but in brief, this is what I did - I can take more photos next time:

 

  1. Put on head magnifier and switch on a desk lamp!
  2. Position the IC and temporarily affix it to the board (can use paper or Kapton tape for that, or two small blobs of blu-tack [temporary putty] at either end - I used the blu-tack this time and was able to very finely adjust the position of the IC by just pressing against the blue-tack)
  3. Solder a corner pin on either side, using regular solder so that the part would stay in position, and then removed the blu-tack
  4. Apply a thin long bead of flux along the pins (I actually applied some liquid flux because I couldn't find the syringe of paste, but then 10 seconds later I found it - so I had a mix of both!)
  5. Feed some solder into the spoon tip until it is nicely convex (I didn't make it bulge a lot, perhaps just 70% of capacity, I'll explore that more next time)
  6. Place the tip so that it was touching the board for helping with position support, and then angled down so that the blob was into the pins, and just ran the iron along! In a couple of places where I thought it wasn't adequately soldered or there was a bridge, I just repeated in that area using the same method.
  7. Dab with a half of a dry wipe to soak up some of the flux, and then put a few drops of isopropanol (isopropyl alcohol or IPA) on the board, rubbed with an antistatic stiff brush, and then wiped it all off with the clean part of the wipe.
  8. Using a thin scalpel blade (very small, surgical type), and with the head magnifier on, using the unsharpened side of the blade, i.e. sharp side up, I pressed against the side of each pin (the thin scalpel blade flexes slightly) to confirm it was stuck with solder, and did that for each pin - it doesn't take long to do this, and gives me peace of mind rather than having to troubleshoot with potentially unsoldered pins later.

 

I have no idea if my technique was entirely correct or not, all I can say is that it was far quicker than soldering each pin individually, and the result visually looks good I think.

It would be great to learn any tips, and about other peoples drag soldering or alternate techniques for surface-mount too!

 

Second attempt

This time around I recorded it, this is uncut from start to finish:

Parents

  • I also find that if I'm trying to sort out a solder bridge (normally after reflow when there was too much paste) that dragging along the pins away from the IC works well too. QFN is my nemesis these days! Very limited possibility of drag soldering there.

  • in reply to Fred27

    I struggle with those : ( has discussed using a hot-plate method for SMD, so I hope to try that sometime, currently I use a pre-heater (with quartz tubes, it doesn't blow hot air), and hot air from above, but the result isn't great, I think because my hot air tool has too small a nozzle and the equipment is just not powerful enough. But I did recently purchase low-temp solder paste as (hopefully if it works) a quick fix, in the aim of then getting enough heat with just the pre-heater and no hot air from top.

  • in reply to shabaz

    I have a hot air gun for this which I hope will be sufficient: I think the secret is tiny amounts of solder and plenty of flux.  Some do, at least, have leads that extend onto the side.  It's partly why I was asking about checking connections/bridges below as you'd want to make sure that the centre pad hasn't bridged or that solder hasn't bridged pins under the package that you can't see.  I suspect the likelihood is high on first attempts!

  • in reply to Andrew J

    Ah, I see. I believe (not 100% sure!) that bridges will be unlikely to occur if the right amount of paste is applied, but I don't know of a way to do that without a stencil. So probably the stencil is important for QFN styles. I recorded a video a while back of how I did it for a QFN microcontroller, and I managed to get all the boards working, but certainly there were some pins disconnected since my equipment is underpowered or poor technique, and I had to fix them with a soldering iron since the connections were visible from the sides. So this video is definitely not best practice! : )

  • in reply to shabaz

    I reckon that the key to re-touching surface mount parts is to use lots and lots of really runny flux. I use the Warton metals Future 315 from Rapid Electronics, and it's just like water in terms of viscosity.

     

    A good splosh of that and I can easily take solder off one pin where there may be too much or add it to another where there is too little using a small conical tip - I only use the spoon tip for the first soldering of TQFPs now.

     

    MK

  • in reply to shabaz

    I thought a stencil for this one definitely.  I used one as an experiment last time I soldered a board up and it went well, although I had managed to hand solder that board on previous iterations.

Comment Children
No Data