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Posts tagged “SMT

Here’s how I do my SMD PCB assembly

I design a lot of PCBs, and assemble most of them myself. Small quantity PCB fabrication services have become so popular and abundant, I take full advantage of them.

Recently I use PCBWay a lot. Their pricing is close to the lowest (sometimes is the lowest), but the quality is still quite good. My favorite part of their service is that they offer different solder mask colors without extra charge. I don’t like green PCBs so this is a big plus!

For small boards for prototypes, batch based PCB service such as OSHPark still wins, as the shipping cost is much lower than from China. I use OSHPark for boards up to 2 sq inches, and PCBWay for larger.

Oh and PCBWay (and some other Chinese PCB fabs) offer stainless stencil for a very reasonable price. I can usually add one for $10 and it is very nice to receive PCBs and the stencil together.

Here are the photos from my typical PCB assembly using the nice stencil.

Step 1: Gather All Materials

Step 1: Gather All Materials

Clear your work area and gather all components, material, and tools. Preparing the organized BOM printed helps to reduce errors.

Step 2: Frame the PCB and align the stencil

Frame the PCB and align the stencil

I use squares made of fiberglass to secure the PCB to the desk. Then overlay and align the stencil on top, and secure it with a piece of masking tape.

View from the top

Compared to Polyamide (orange plastic film) stencils, stainless stencils are easier to align to the PCB. The pads kind of “snap” into place.

Step 3: Squeegee time

Ready to stencil

Now it’s time to spread some solder paste onto the PCB. Use plenty of paste and pull the squeegee at a steady speed.

Here the stainless stencil really shines, as the paste spread very smoothly without effort.

Solder paste printed

(Ok, I could’ve done a better job, but…)

Step 4: Ready to Pick & Place

Solder paste printed

Now the PCB has solder paste beautifully printed on, I’d get busy placing components.

Step 5: Ready to Reflow

Ready to reflow
Here the boards have all the components placed and ready to reflow. Sorry I forgot to take photos during the pick & place process.

I use a small reflow oven to reflow PCBs.

 

 


SMT Soldering 101

I get a lot of questions regarding surface mount soldering. The thing is, with the right tools and a bit of practice, SMT (Surface Mount Technology) soldering is really not difficult.

First, please view this excellent video created by CuriousInventor.com (no affiliation. I just like this video very much). I’ve been doing SMT soldering for a while now, but was very impressed with the techniques shown in this video.

Here’s the list of tools/material you need:

  • Temperature controlled soldering iron/station (such as Hakko FX-888. Standard size tip works fine.)
  • Thin soldering wire – 0.015 inch (0.4 mm)
    Regular 0.03 inch (1 mm) gauge solder wire is too thick for small SMDs. A very common problem with SMT soldering is to apply too much solder. Small parts like 0603 resister only need tiny amount of solder.
  • Flux – pen type flux such as Kester 951 recommended. Apply generously – it will dry out quickly and does not harm the PCB.
  • Tweezers with small tips – get a good pair that’s confortable to use.
  • Magnifying glass – you can’t solder if you can’t see. I wear magnifier visor (OptiVisor #4).
  • Good lighting – you need much brighter lighting then reading a book to see the small details of SMT soldering.
  • Solder wick – as excess solder is the enemy of good SMT soldering, you need solder wick to remove excess solder. Perfectly soldering fine pitch packages like QFP is very unlikely without a help of solder wick. Thinner one like 1.5 mm wide is easier to use.

Traditional through hole technology is phasing out, and so many new devices are not offered in through hole style. Learn to solder SMT will broaden your choices.

(Let me know if I forgot to add anything here.)