Thursday, February 28, 2013

Dangerous Prototypes QFP breakout board tips

Today was my second attempt at using the Dangerous Prototypes QFP 0.5mm pitch breakout board to solder  LQFP-64 IC.  My first attempt was messy due to a slight misalignment of the pins. Today's attempt was more successful.

Almost everyone agrees the general workflow is to tack down two opposite corners with a soldering iron and when alignment is verified use your favorite technique to solder the remaining pins in place. But getting the IC perfectly aligned (and keeping it there while tacking the corners) is tricky.

Two things I figured today:

1. The solder mask can act as a physical alignment guide. Put the IC approximately in place and then firmly push down on the IC and attempt to slide it up and left (assuming the normal orientation). You'll find that when the IC's pads reach the solder mask there is resistance to this sliding motion. At this point the IC should be perfectly or nearly perfectly aligned. [Update 4 Mar 2013: this worked just fine with an Analog Devices ADAS1000 but I just tried this with a smaller 32 pin package and noticed the IC's pads were shorter so this tip didn't work: so this is very much package dependent.]

2. Next while keeping the IC pinched firmly in place I used a washing line peg to clap it in this position. I found the peg applied enough force to keep it reliably positioned, yet it was still possible to nudge it slightly should the alignment need adjustment.

I then tacked two corners, removed the peg and soldered the rest of the pins.

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