[gta02-core] Openmoko Beagle Hybrid

Christoph Mair ml at chonyota.net
Wed Jun 16 23:24:25 CEST 2010

Hi Joerg!

Am Mittwoch 16 Juni 2010, 21:51:53 schrieb Joerg Eesmann:
> Hi Nikolaus,
> Very good stuff, an open phone with OMAP3530-Power, my dream...
> I am a little off topic here, but I take the chance to ask eitherway.
> I am thinking about a little simpler NaviBoard.
> The actual Naviboard has 2x2 ADC with I2C and one 2axis Gyro(analogue)
> and one 1-axis gyro(analogue). A few weeks ago Sparkfun announced a new
> 3-axis gyro with I2C (IDG3200), which would make the Naviboard much
> simpler, I guess, and give the chance to add the pressure sensor
> (BMP085) to the PCB.
I'm working on this. See my announcement mail. :)

> I have one of these gyro on a breakoutboard in my hands, the chip is
> really tiny with a tiny tiny footprint.
> I think I will be able to solder the pressure sensor with a reflow oven
> in future (when my reflow oven is finished), but this gyro and the
> honeywell mangneto sensor. How do I solder them?
> How do I apply the solder paste to such a fine grid with no special
> epipment?
> You said, you also have at least one chip with BGA (0.5 pitch I guess)
> on your board, how did you manage to solder this during prototyping?
> Any tipps?
> Anyone?
Well, I reflow soldered the HMC5843 which is a 0.5mm pitch QFN. The steps are 
rather simple:
- get a good PCB with the right footprint and soldermask
- if you want to use solder paste, just apply an amount on the pcb and melt it 
with your solder iron. This should result in small dots of solder on the PCB. 
It's like a BGA, but with the balls mounted on the board. Working with solder 
paste but without stencil mask won't work for fine pitch applications. Just use 
normal solder wire for this task. It works equally well.
- flux should not be necessary, but YMMV. 
- carefully place the QFN onto the solder drops. Make sure it aligns with the 
pads. Very small alignment errors will automatically be corrected during the 
reflow process.
- place everything in your oven
- recheck the alignment
- heat the oven up until the solder melts. I used a piece of solder wire next 
to the board to see if the melting point was reached.
- switch the oven off when you think it's done. The extra solder wire should 
look like a ball now and the chip should be sunken onto the surface of the 
PCB. Don't wait too long!

That's it! good luck!


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