The ATMega328P-MU Via problem

Hi guys, I recently designed a PCB that includes an ATMega328P-MU chip in it, I had it printed and everyting else seems to work fine. I noticed however, a special detail I had not forseen when I designed the PCB:

There are vias and trough holes in the inside part of where the ATMega chip is supposed to go. (so there are little copper holes). The problem is that the chip itself for some odd reason has a giant ground square pad in its bottom part. Which (I think) will short out all other vias. (I am not sure of this and I have to try to place it bare on the board)

Anyways, I was wondering if any of the possible things are doable to fix this:

  • I tried putting electrical tape, melted, I cant burn any bootloader on the chip cause it says it cant find the chip. (Im assuming then that the tape somehow didnt let some of the pins connect.

  • I was thinking of grinding the board down just a milimeter or less with a dremel, but I am not sure if this will fuck up the board or not. Is this doable?

  • Is there some sort of paint thats non-conductive that I can put over these little copper holes so that I can then place the chip over them?

  • Any suggestions/ Ideas to fix this?

teflon will not melt, or prabably a small very thin piece of mica might work. Mica can be spliced splitted into very thin slabs.

both are/were often used to mount a to220 package isolated to a cooling piece of metal.

You must have used the wrong package footprint - that ground pad should have been an exposed pad on the board.

You have a problem, TQFN pads need to be flush with the board really, since you have to be very frugal with solder paste to avoid risk of shorts. A fine lacquer of some sort? (This is what soldermask is). If you are only dealing with 5V it can be a very thin coat.

Note that the datsheet says that the exposed pad should be soldered to ground....

MarkT: You must have used the wrong package footprint - that ground pad should have been an exposed pad on the board.

You have a problem, TQFN pads need to be flush with the board really, since you have to be very frugal with solder paste to avoid risk of shorts. A fine lacquer of some sort? (This is what soldermask is). If you are only dealing with 5V it can be a very thin coat.

Note that the datsheet says that the exposed pad should be soldered to ground....

nail polish paint? (according to Wikipedia: ail polish is a lacquer applied to human finger or toe nails to decorate and protect the nail plate. The formulation has been revised repeatedly to enhance its decorative effects and to suppress cracking or flaking. Nail polish consists of an organic polymer with various additives.[1])

Kapton tape is good to 260C. 1 mil is .03mm.

Your PCB manufacturer might do “capped vias” so they may already have the same insulating layer that’s on the rest of the board. All in all though it sounds like you need to scrap your boards and just accept it as a learning experience.

I useds nail polish, and I think it worked. I mean i placed the chip, checked for any solder shorts on a microscope, checked that all pins were connected, all good. Powered it up, nothing seemed wrong.

Connected the ISP cable, went to atmel studio, detected atmega328p, uploaded optiboot bootware from arduino. upload complete.

The only problem I am having now is every time I try to upload code to the chip via the FTDI I always get the stk500_getsync() error. 0x00

all the time, I've tried pressing the reset button as some say but still nothing.

Your boards will never work reliably with a badly mounted chip.

Scrap the boards, and fabricate some new ones with the correct footprint.

// Per.