How to fix QFP-144 package if you forgot the bottom ground pad on PCB.....

[Altera_Forum]

Our circuit board layout person forgot the mandatory ground pad underneath a Cyclone III EQFP-144 pin package. As a result, the JTAG byteblaster would not connect until it is grounded. None of the ground pins on the chip seem to be connected to that pad. Rather than drill a hole thru the bottom of the circuitboard and somehow solder to the ground pad (shorting out layers in between), we found a better solution.... 

  At each corner of the package, the ground pad is connected to a part of the lead frame (called the 'paddle' that holds the die), the tiny end part of it is barely visible flush with the package epoxy molding on each corner of almost any chip package. We used a tiny .0225 drill bit from Harbor Freight's tiny drill bit assortment and holding it parallel to the plane of the board dug in straight down at a 45 degree angle until we could see more of that corner part of the lead frame. Next, we simply soldered a wire to it and ran it to ground. The chip now is recognized by JTAG and everything works! (See attached photos)  We successfully saved all 10 of our prototype boards with this method and it only takes a few minutes to do. At least we can continue on to find more problems before doing a new board spin.  I think it's better to drill and solder to any corner but the 'pin 1' corner because the lead part on that corner is forked so less area to solder to, as shown on the two leadframe picture attachments below.   The only thing I was worried about is that ground pad on the package could short out un-tented vias and traces underneath the chip, but it seems the pins on the chip are slightly taller holding it up a tiny bit above the board, so everything seems to be OK.

[Altera_Forum]

I like this. It has caught me out in the past and I'm sure it will again - even though I know about it...