smd soldering

I think I am getting pretty good results with through hole soldering so I figured I would try my hand at a little smd practice, it's not looking so nice.


as you can see in the pics I get blobs instead of nice joints. I am assuming that is due to using too much solder, but the other problem I am having is that the smd parts are so small I can't touch them with the iron or they will move around, so I'm basically putting the component on the pads, heating the pads, putting the solder on the pad until it flows and holding my iron there hoping the solder heats the components. leading to too much solder (I think)

what do you think?

Hi,

I think you'll be MUCH happier using solder paste. It holds the part in place and flows quickly. Using a hot air pen makes that part easy.

I'm sure those with more experience than I will help out too...

My method:
Very small diameter 60/40 solder <= 1/2 mm.
Liquid solder flux on Q tips.
Small to medium diameter soldering iron tip, set to ~380’C
Offset tweezers.

With Q tip apply a small amount of flux to SMD PCB pads, let dry.
Apply a very small amount of solder to one ‘only’ PCB pad.
With the tweezers, position an SMD device near the PCB pads.
Heat the previously tinned pad, slide the device in place, keep all feet flush to the PCB surface.
Apply very small amount of solder to the remaining pads/feet.
(reapply flux as needed and reflow solder)

Clean work with Q tip soaked with isopropyl alcohol.
(or soak in alcohol then immediately rinse in water. Blow dry with compressed air).

Glue larger SMD devices to PCB, let dry, solder as mentioned

I always use a small amount of liquid flux, others don’t.
.

Mine:

  • apply just a hint of solder to one of the pads
  • hold the component with tweezers and place it while heating that join (keep the tip clean and slightly solder-wet)
  • zap the other side
    -come back and zap the first side

I would use solder paste but I worked in a factory and they treated it like it was plutonium. Actually, two factories, and they both did.

My tip for repairing SMD IO is to use soldering grease (AMTECH NC-559-AS is very good for that), apply hot air ~300’C for tin with Pb and about 380’C for PB free (you have to have rework station) and that’s it. The best result can be obtained with applying hot air in two steps, to preheat first for 5-10 seconds and after short time to heat-up to tin melting. Soldering grease is able to clean with the propylalcohol or with just normal alcohol.

I go with Aarg. Don't try to solder the pins individual but the whole row. Because of solder mask most solder will just flow to an pad. And if not, just use a bit of solder wick an tada :slight_smile:

If I may attach myself to this question: I would like to get a little more into SMD soldering. To separate sites of boards, to get the board smaller, to be able to use parts that are not available as DIPs.

My budget isn't too high, I would like to stay below 50€. Would you rather go for

Do you think it is possible to use this for QFN packaging? I am especially interested in the TPS63001.

I am also not sure if I understood the necessity of a stencil. Does it just make your life (much) easier, or does it actually enable you to do stuff you are not able to do without? Looking at the mess this guy SMT soldering on a hotplate at sector67 - YouTube made (which still kind of worked for most connections), it seems that it is well possible to apply solder paste by hand. That would be great, since a stencil is two or three times the price of those cheap China PCBs ...

aarg:
Mine:

  • apply just a hint of solder to one of the pads
  • hold the component with tweezers and place it while heating that join (keep the tip clean and slightly solder-wet)
  • zap the other side
    -come back and zap the first side

+1
It is method I have used in R&D lab.
To desold use two iron : one on each side of component and when solder is liquid you lift both irons with the component in the middle.

No air gun is necessary.

To clean up all those pins, simply flux them liberally and then apply a clean chisel tip to them. It will remelt the solder and the flux will flow it more evenly. That’s very easy to clean up. You’re 90% of the way there.

The way to do this in general (from the top) is this:

  1. Use a chisel tip!
  2. Use a chisel tip!
  3. Use a chisel tip!
  4. Flux the pads and pins liberally.
  5. Wet the chisel tip with a liberal amount of solder.
  6. Hold the IC down with tweezers or your index finger or whatever works for you and make sure it is aligned correctly. Then bring the solder on the chisel tip to a corner pad/pin. This is not what you normally want to do for through-hole, but it works well here. Do it with the other corner pin. This is called “tacking it in”. One hand on the IC, one on the soldering iron for this step.
  7. Now that the IC is tacked in, do the other pads. You can either bring the solder to the pins on the chisel tip (one handed!) like you just did or can solder directly with the roll of solder (one hand on the solder, other on the iron).
  8. Anything that doesn’t look good, clean the tip, apply flux, and just use it to reflow the nasty pin.
  9. For the two-pin devices, tacking one side is fine, then solder the other, then reflow the first side. That is what works for me.

Takeaways:

  1. Use a damn chisel tip.
  2. Use lots of flux.

This IC was done using this technique. Your components are a lot easier to solder.

PIC24 SMT Soldering Closeup.jpg

Watch this guy drag-soldering the big QFP around 2:00. That's what I try to do. Tack the IC in, then drag solder the rest of the pins. Lots of flux and a chisel tip is necessary.

People think a fine soldering tip is necessary for fine pitch SMD work. It's not true, in fact it is very counterproductive. Use a chisel tip.

If you're going to be doing a lot of boards with that number of components I would suggest it's really worth looking at a DIY reflow oven.

I put one together with the cheapest oven from my local Argos shop and a Rocketscream reflow controller.

I've since upgraded to a proper desktop reflow oven and to be honest I think I was getting better results with the DIY solution.

To be used with solder paste and a stencil

We do that regularly. 4-elememt/1500W toaster oven. Kester EP256 solder and Pololu.com stencils (until we start cutting our own anyway, tried some that other posters volunteered to make for us and we’re thinking of following suit).
No oven controller, just a thermocouple probe with a DVM, keep an eye on the temps and monitor/adjust by hand.
Ramp to 125-150C for 90 seconds, ramp to 185-200C for 90 seconds, cool down. Do some trial runs to get a feel for how long the time periods take to achieve, and how much to back off and when to not exceed the temps.

Attached is solder profile typical for SMD parts.

Solder_Reflow_LeadFree.pdf (365 KB)

You are probably right. Maybe I should invest into a cheap oven instead of a heat gun (on the other hand, I really hoped for an easy method to shrink shrinking tube ;)).
Can somebody suggest a model that is available in Germany? This one is the cheapest one on Amazon:

JoeN:
People think a fine soldering tip is necessary for fine pitch SMD work. It's not true, in fact it is very counterproductive. Use a chisel tip.

Truer words were never spoken.

Search youtube for smd soldering - I found a number of very good tutorials in the past that showed a number of techniques. See which one works best for you. They all basically come down to everything needs to be clean and have flux so the solder will flow correctly. You also have to avoid getting the joint too hot or it simply causes problems - the solder should melt and flow easily without having to overheat the joints.

aarg:
Mine:

  • apply just a hint of solder to one of the pads
  • hold the component with tweezers and place it while heating that join (keep the tip clean and slightly solder-wet)
  • zap the other side
    -come back and zap the first side

I would use solder paste but I worked in a factory and they treated it like it was plutonium. Actually, two factories, and they both did.

Lead-free no-clean solder paste is the thing to use. They were rightly paranoid as dry paste can form
dust in the atmosphere and lead-rich dust in the lungs is essentially there for life, continually poisoning.

A converted IR toaster oven can be a very handy reflow-oven - you need some kind of temperature
control. I use one and simply watch for the paste reflowing, no need for a timer/controller. Way way
better results than hand soldering.