Electric Griddle Reflow Soldering


Below are the steps I took when reflow soldering my circuit board.

Step 1: Apply solder to the board

Using the solder paste turned out to be very easy. The first bit of solder paste that came out of the syringe was dry and, in my opinion, not useable. I discarded the dried solder paste and continued squeezing solder out of the tube until I found the saturated (I believe with rosin) paste.

Solder Application Palette
Solder Palette and Tools
To apply the (good) solder paste, I first made a 'palette' of solder by squeezing a small dime sized amount of solder paste onto a piece of paper. I then dabbed the tip of the syringe into the palette, and collected a small amount of solder on the tip. I then 'painted' all the surface mount solder pads I needed to solder (except the 28-pin QFN package).

I did not add any solder to the 28-pin QFN solder pads. The board came from the factory pre-tinned, so all I did was let the tinned solder reflow onto the solder pads of the QFN component. You could in theory do this for all the components on the board, but it seems like a good idea to have more solder on the component if you can manage it.

Solder Application (painting)
Applying (Painting) the Solder

Step 2: Place Components

Placing the components was rather straight-forward. I just had to be very mindful of which components went where, and how much caffeine I'd had. As long as the components are placed in the solder on the appropriate pads they reflowed nicely.

Step 3: Crank it Up

After all the components were placed, it was time to reflow! I did all the solder application and component placement on the griddle surface, so all I needed to do was move the board on top of the heating element and crank up the heat. The electric griddle heated up very fast, and very hot.

The griddle heat adjustment knob has markings up to 400 (I assume it's degrees F), while the solder paste has a melting point of 430 degrees. I was slightly concerned about not melting the solder however, in ten minutes the board had completely reflowed. I'm guessing the griddle has a poor sense of temperature (good for melting metals, not good for cooking breakfasts.)

How to know when the board is reflowed? When you apply the solder paste, you'll notice that it has a non-uniform color to it. It's as if there are a bunch of little solder shavings suspended in rosin flux. Well, I think that's just it. It's a bunch of a solder pieces in flux. Therefore you can see the grainy-ness of the paste. When the board is reflowed, this solder will look like molten metal with a completely uniform and shiny surface. You can also expect to see rosin boiling out of the solder, and raising as fumes -- it's best not to breathe these vapors.

Electric Griddle Solder Reflowing!
Electric Griddle Solder Reflowing!

Step 4: Let Boards Cool

After the boards cooled down significantly I hand soldered the remaining through-hole components (tri-color LED, switch, power connector) and the components on the bottom side of the board (pin header, crystal).

Step 5: Enjoy Fruits of Labor

All in all this only took about 2 hours from start to finish -- and was extremely painless and fun. The next time I reflowed a board it only took 30 minutes. I'll certainly be using this method more as I create more prototype boards.

finished circuit boards
Finished Circuit Boards
finished circuit boards
Finished Circuit Board with LED

project added: 5/4/2006

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