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Trial manufacture of surface mount board using solder paste gun

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Solder paste gun(Soldering Gun / Solder syringe?)

My old ways

My old way of reflowing surface mount boards.

  1. Apply solder paste to the substrate.
  2. Place the parts on top.
  3. Reflow on a hot plate.

Follow the steps above.

If there are many parts on the board, or if there are many boards to be mounted, the solder paste is printed on the board using a stencil as a method of applying the solder paste to the board (1).

Printing solder paste using a stencil

But, for the time being, in the case of just 1 or a small circuit, making a stencil is expensive and troublesome. So, I used to apply a little bit of solder paste to the tip of a toothpick or thin screwdriver and spread it on the board.

My old way ↑

However, if you apply it on the board after putting it on the tip of a toothpick, it is very difficult and troublesome to apply a stable amount.

Generally, you put solder paste into a syringe and apply it little by little.

It's like this video.

Solder paste in a syringe

So, I bought a type of solder paste with a syringe.

Solder paste like this.  When I bought it, I found out that since the viscosity of the solder paste is high when I use a thin needle, the resistance of the solder paste passing through the thin needle is high, and the solder paste does not come out unless I push the piston very hard.  My physical strength was worn out, so it was inconvenient.

Encounter of fate

It came suddenly.  When I was shopping on Aliexpress, this happened to appear in the recommendation column.

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Whoa !!Isn't it the gun that can be used for soldering paste that I always wanted?  If Ⅰ pull the trigger like a glue gun, a lot of solder paste will come out. I'm sure.

I bought it quickly.

The quality of plastic is not good, but it doesn't matter.

If you pull the trigger like this, the piston is pushed out.
I put the solder paste in the syringe right away.

Fits perfectly.  Why not?

Use for the trial production

Use this gun

I just received the board for the step-up DCDC converter of the newly developed solar cell experimental set, and I wanted to make 1 and test them, so I will use this gun to apply solder.

When you pull the trigger, solder paste comes out.  The trigger is a little hard because the solder paste passes through the thin needle.  However, it is much easier to apply than pushing the syringe piston.  This is convenient.  Gun type is wonderful.

However, the pressure remains in the syringe, so even if you return the trigger, the solder paste will come out from the tip of the needle for a while.   It is similar to glue guns.

So, in order to apply an appropriate amount to each land of the board, you need some tips such as the amount of pulling the trigger and the timing to release it.  If you do it several times, you will gradually get the knack.

Reflow with parts on top

Now that the application of the solder is complete, we will place the parts with the reverse action tweezers.

Engineer's reverse action tweezers PT 28 is an essential item for me.  You can put parts very easily.

Reflow on a hot plate and solder the rest of the parts that require hand soldering. The prototype is completed.
Will it work?


If the brightness sensor (CDs) is judged to be bright, the LED does not light because the DCDC converter does not boost.   Three LEDs in series.   With a 3V battery, the DC-DC converter does not work due to insufficient voltage.  This is as designed.

When you make a shadow on the brightness sensor with your finger, the DC-DC converter operates to generate 9V when the sensor judges that it is dark.  Because the voltage has risen, three LEDs connected in series also light up.  The exam is successful.  The board was perfect.

Solder coating using a stencil

Since the prototype worked well, I will make a lot using stencils instead of guns.

Printing of solder paste

Fix the 8 facing boards to the center.

I'll put a stencil on it.
Adjust the position and secure with tape.

Prints solder paste.

Solder paste can be printed more neatly at once than with a gun.

Place the parts on a hot plate and reflow.

The board is completed by soldering the parts that require hand soldering.

Kim wipe and absolute ethanol to clean the stencil

First time purchase

This is my first time to buy Kim Wipe.  Kim Wipe looks like a tissue, but it's like a special tissue that doesn't produce dust when you wipe it.

Soak this in absolute ethanol and wipe off the remaining solder paste on the stencil.

For some reason, only this 500 ml type of anhydrous ethanol was sold.  In addition, the mouth is as big as a pet bottle, so it is inconvenient to drip an appropriate amount on a Kim Wipe. So I bought this bottle at a 100 yen shop.

It was a product name of one push dispenser bottle.
If you put absolute ethanol in this bottle and push the round Kim Wipe from the top to the bottom, an appropriate amount of absolute ethanol will soak into the Kim Wipe.
Very convenient.
The person who invented this bottle is a genius.

Cleaning stencils

The combination of Kim Wipe and absolute ethanol is the best.
If you push a little more absolute ethanol 2 or 3 times and wipe it off, the solder paste stuck to the edge of the small hole will come off cleanly.

This Gun is wonderful.

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This gun was very useful for applying solder paste to surface mount boards.
I'm glad I bought it.
There are several kinds of needle tips, so you can choose your favorite thickness.

2019.11.16 PS : I found a cheap and super optimal nozzle!

↑ Postscript

You can buy a solar cell experimental set with a DCDC converter, which was made experimentally using a gun, here ↓ ↓.

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