electronut Programming & Embedded Systems - by Mahesh Venkitachalam

Soldering Accelerometer MMA7660 in DFN-10 package using a Hot Air Rework Station

Freescale makes some nifty accelerometer chips, like the popular MMA8452, for which Sparkfun, USA sells a breakout board. But unfortunately (for hobbyists) they all come in hard-to-solder tiny little packages, like the 16 pin QFN which is just 3 mm x 3mm across.

After a few unsuccessful attempts to solder the MMA8452 chip at home, I found a better candidate - the MMA7660 which has a DFN-10 package. As you can see from the schematic below, the latter has only 10 pins, and the pins extend to the sides, which makes it easier to solder.

[From Freescale MMA8452/MMA7660 datasheets, for illustrative purpose.]

I was able to successfully solder the MMA7660 on to DFN-10 prototype board using a hot air rework station.

I basically followed the technique shown in the video below:

  1. Apply flux and tin the pads.
  2. Place chip on tinned pads - align correctly, apply flux.
  3. Heat the chip with the hot air gun.
  4. Solder exposed pins on the sides.
  5. Reheat the chip with hot air gun to reflow the solder.
  6. At each stage, inspect pads with magnifier for shorts, and use flux generously.

Sjaak solders a QFN chip, attempts a BGA chip:

A couple of photos of the chip after soldering:

So why torture yourself soldering these microscopic chips when you can buy breakout boards?

A few reasons to consider, especially if you are trying to make a product that you might sell:

  • Cost: The breakout board is usually 4-5 times more expensive than buying the chip.
  • Size: If you are designing a PCB yourself, it's going to be much more compact if you just use the chip and not the whole breakout board.
  • Bragging Rights: When you walk into a bar and announce that you hand soldered a DFN-10 chip, that will surely make you popular. Right? Right? ;-)

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