Cpld rework / removal

[bnice7]

How are you all removing the Cpld? I have one board that's being problematic and I want to pull the Cpld to make sure there's no solder or leftover flux in the wrong place underneath the IC. I read the data sheet and it states the max. soldering temp is only 220C. I've never used hot air set to that low of a temperature before to remove an IC, and worry about lifting pads. Would I be better off using that low-melt solder?

The issue I'm having is no boot with a 3.1 ROM, and Diagrom hangs at "Checking if a 24-bit address CPU is used". The CPUs are good, I've tried a few -- they are tested and working in two other TF536's that aren't having issues.

THANKS!

[PhilC]

@bnice7 it sounds like you've either hot some loose or bridged pins on the cpld.

The solder I use is leaded and has a melting point of 183oC so you can solder at 220. I've used hot air at 300 and the chips have been fine. Obviously I heat them for as short a period as I can.

[bnice7]

Thanks @PhilC , I'm also using leaded 63/37, just wasn't sure if it would be safe to use 280/300C with the hot air station. I'll give it a go then!

I'm thinking the same re: loose or bridged pins. Visual inspection looks good and I did go around with a multimeter to check for bridges, and also re-flowed it a few times, but I know there's some vias close to some of the pads underneath the chip, so figured I'd get this one off the board and check it out. I ordered a few more Xilinx's just in case I do have to replace it.

[8 Bit Dreams]

Will be hard to remove it without bottom heating - it's four layer board..
chip will go off much easier if it lays on something warm, so middle layers will not absorb too much heat

[bnice7]

Yeah I don't have a preheater, so I just preheat the board using the hot air at a distance for a little while. I managed to get it off but it did take quite a while even at 300C, probably a little over a minute. Hopefully it's still good. I'm not really seeing anything that looks suspect, aside from some little pockets of hardened flux that worked its way under the chip. I'll give the PCB and the cpld a good cleaning and try to solder it back on later, then re-flash the firmware for good measure. Thank you for the suggestions.

[Danoo]

A cheap pre-heater is certainly the way to go, once you have used one you will probably wonder why have I not ever purchased one previously. Makes CPLD removal a simply process. The unit I use only cost the price of 2 CPLDs, and has probably saved me purchasing a lot more replacements than that. :)

[bnice7]

A cheap pre-heater is certainly the way to go, once you have used one you will probably wonder why have I not ever purchased one previously. Makes CPLD removal a simply process. The unit I use only cost the price of 2 CPLDs, and has probably saved me purchasing a lot more replacements than that. :)

@Danoo whaaat! That sounds really reasonable... I'm trying to not spend too much due to the fact that I lost my job back in July, but I'm definitely curious for that price. I thought they were much more expensive than that.

I ended up drinking too many beers trying to make it through our presidential debate here in the good ol' US (was a total s***show, as expected), so I haven't spent any more time today on this problematic board, but I'll post back here with some photos if I still have issues in the morning after re-soldering and re-flashing the Cpld.

[Danoo]

The cheap unit I picked up was a YIHUA 853A pre-heater, about 18 months ago for about $100 AUD (71 USD) :D

pre-heater.JPG

[bnice7]

I just wanted to provide a quick update on this thread in case anyone else runs into similar issues. I pulled out the TF536 and tried booting diagrom with a 68000 in the relocator. Doing this, I got a different result and diagrom wouldn't boot at all (seemed like it may have been outputting something to the serial port, but I didn't bother trying to hook that up). Then, I removed the relocator and plugged the 68000 directly in the socket, and diagrom booted up with no issues, so at this point I expect the issue is with my relocator. Next, I'll try booting the TF536 in the CPU slot w/o the relocator if I can find another socket to stack it, since this is a rev. 5 board and otherwise the ROM would interfere.

[DominoTree]

Desoldering alloy should let you remove it easily using nothing more than a standard soldering iron (for best results add some flux)