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A project log for Microwave Transmitter

30 - 6000 MHz synthesizer with power amplifier

PeroPero 05/12/2017 at 09:043 Comments

The soldering process went on mostly well, no tombstones, no misplaced components and no excesive solder...however, some bugs were found and caused me a couple of hours of annoyance:

These are all bugs I found so far. I examined the board and believe that it main parts should work properly. I could test out the VCO, attenuator and switches, but I cant solder the Teensy on board before all my reworking is done. So, when new detectors arrive, I'll give it a test try.

Discussions

K.C. Lee wrote 05/12/2017 at 09:45 point

You want to reduce the amount of solder paste to the big thermal pad under your QFN.  Usually it should be around 60-70%.

Vacuum pickup would help a bit on handing tiny parts.

You have to increase the temperature profile of your reflow as the RoHS parts are supposed to be soldered at 260C instead of 240C.  Could also be uneven heating so the area of your DSBGA might not reach the needed temperature. i.e. shadowed by taller parts or just uneven heating because of oven design.  

I have done 4 or 5 similar 3x4 package (RoHS) from TI with hot air rework tool.  It takes a while if the PCB isn't perheated or have a lot of copper under it.

Your solder paste would help the part stick a bit better than me doing that without solder paste as I am too cheap.

https://hackaday.io/project/4993-dual-channel-battery-chargeranalyzer/log/17291-keeping-up-with-the-times-prototyping-with-qfn-and-bga

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Pero wrote 05/12/2017 at 13:38 point

hanks for the feed back, those were my findings as well. I
don't think I'll use reflow oven at 260°C to fix this, as it's a self
made and I'm not really sure if it can reach that temp. I'll try with
the hot plate and air gun. 
Btw, nice documentation of your
earlier project...regarding that chinese company (they seem terrible!)
silkscreen, in my case OSH Park also screwed up a bit. You can clearly
see that silkscreen is off centered from the pads on this BGA chip.

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K.C. Lee wrote 05/12/2017 at 15:34 point

The hotplate would help a lot as that's essentially what the commercial setup do.

As for OSHW, their PCB supplier has much better registration.  My recent batch however, they having some issues with missing gold plating on ENIG.  That one escaped their QC.

The Chinese place is hit and miss, but is a lot cheaper.  I have changed my silkscreen in my layout to allow for the slop.

More on my SMT stuff:

https://hackaday.io/project/6929-smt-assembly-on-the-cheap

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