Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

Need to access the ground slug

Hello All,

I have a board using a Cyclone III EQFP package and the FPGA footprint did not have the ground slug.

I have drilled a hole from the back of the PCB to access the slug. I got access to the slug and can hold a wire between a ground net on the PCB and the slug to make the board function properly.

I want to create a sturdier solution than one person holding the wire and me debugging the board (quite clumsy)

I do not want to solder the wire to the pad because there are inner layers 1.2V and Gnd. In case the solder touches these layers the board will be smoked. The current drill is 3 mm dia.

Has anyone done something like this before (rework) ? I want to do this rework so that I can get most out of the board before the next turnaround and also demo it to the customer.

Any help will be appreciated

Thanks

Ajay

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Hello Ajay,

    I was looking for Cyclone III EQFP board design related posts and found yours.

    I have a possible solution for your problem. You may use a kind of spot welding technique:

    Use e.g. a 47000uF/25V electrolytic capacitor. About one mm2 or thicker wires should be soldered to the terminals of the capacitor. To one of the wires e.g. a 20mm long, about 0.5-1mm diameter (isolated on the sides) copper wire must be soldered. To the other terminal wire e.g. a 10mm long, a very thin e.g. a single wire from a stranded copper wire must be soldered.

    Charge the capacitor with limiting the current and remove it from the power supply.

    The thicker wire of the charged capacitor should be pressed firmly via your 3mm hole to the center pad of your Cyclone III. The other thin copper wire should be touched to the center pad of your Cyclone III. By touching with this second wire the center pad, you will close the circuit and create a high current pulse, dissipating a lot of energy at the location the thin copper wire touches the center pad and it will be welded there. The contact will not be very strong, but will make a permanent electrical contact. You may need to fix this thin wire with glue to the PCB.

    Before doing it on your FPGA board, try it first on scrapped ICs. You may need to experiment with the capacitance, voltage level and wire thickness. Also, ware safety glasses and use tweezers as the wires can get hot. Sparks will also be created, so flammable materials must be removed from the vicinity of this work.

    I hope it will help.

    Other - I am starting a Cyclone III EQFP board design and to increase the chance of success I would like to see other similar designs. I would like to ask you to send me your board design/layout files. My Email address is: jsar(at)freemail.hu

    Thanks,

    Janos