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SMD soldering

Do you soldering with SMD elements
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The problem
Surface Mount devices nowadays have pin pitches down to 0.5mm, that is, you get two pins each 1mm. You may have good eyes, a steady hand and balls of iron, yet as a human you will not be able to individually solder these things. How do people make prototypes or small runs of designs using Surface mount then? Read on, because we will now solder a 0.5mm pin pitch device in a couple of minutes using tools normal humans can afford.

Your soldering iron

You might think you need a needle-pointed soldering iron for this fine work. Not at all. In fact a spade-head bit for your soldering iron is ideal, like mine pictured above. What is that metal tube on top? This is my de-cancerifying tube. As you can see below it is connected by a flexible pipe to a big silver machine made by Purex.

This beast roars a motor deafeningly, creating a vaccuum which sucks the solder and flux vapours through a purifying filter. I have a second black box, on the left of the picture, to filter anything that escapes. And still, even with these precautions, my work room stinks of solder and acid flux after a building session. I must have so much lead in me I am surprised I don't set off airport metal detectors. Anyway, please take some precautions not to breathe that stuff in, it will certainly give you some kind of horrible cancer if you get too much of it in you.

Step 1: Position the device
Here is the bare PCB.

You should always do the most difficult components first, and the flattest components first.

Step 2: Tack two corners with solder
No need to be too careful, but check your pin alignment AFTER THE FIRST blob of solder. You will still be able to adjust it. When you place the second blob, you are committed. Get it right.

Step 3: Drown in solder
Warning, balls of iron required. Say your prayers and trust in Numbnut. (At least you can be certain that I exist).

Lay the solder along the pins and gently run your iron along it. Do NOT drag the iron along the pins, they will be fatally damaged. Gently melt the solder into the pins without force. Ensure completely covered, like a kids icecream under his favourite sauce.

Step 4: Get your braid
Use high quality solder braid as shown below

Step 5: Lay the braid along the pins

Another mysterious manifestation of the Hand of Numbnut guides us on our way. A sign!

Make sure you allow some excess braid at the end, the solder will travel up it.

Step 6: Suck up the excess solder with the braid
You gently - GENTLY - head the braid without placing pressure on the pins. If there is difficulty melting the solder through the braid, melt a little bit of solder on your side of the braid to help with the initial heat conduction.

Run the hot iron along the braid, the solder will leak up into the braid leaving lovely clean joings without shorts. You may need to hit it with multiplepieces of clean braid to get it completely clean.

What you do NOT want to do is start tugging to get the braid off because the solder has solidified. Back off, let it all solidify and run the iron over it again - without pressure - to get the solder molten and the braid moving again.

When its done, it looks like this:

Step 7: Check NOW
Check NOW that you are in a good situation. If you miss a short, it might cost you days to track it down, yet at this moment you could fix it in seconds. Get it right EARLY and it will save you from much unhappiness. Do NOT leave it for later because you are in a rush, or you are bored and wish thing thing was over so maidens could peel grapes for you and massage your back. You will pay a terrible price! Heed the warning words of Numbnut!

Using a lamp can give good feedback:

You can see we might have a problem in the bottom left, in fact it was just some flux residue. The saintly thumb of Numbnut beams upon us, Numbnut is pleased with our work.
Step 8: Sanity check
Before you apply power to a prototype you just built, you should ALWAYS check the Vcc and GND nets to see if they are shorted together. many chips have these pins next door to each other nowadays, they are easily shorted. This 10-second check can save you weeks of horror and despair.

That's it, best of luck!
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