S9 Hashboard repair: swapping chips

[dext0rb]

Hi all,

Can anyone share some techniques/tips on how to swap chips on these hashboards.

I have a pile of donor boards and I'm trying to take some bad boards and make then good boards by swapping the good chips in.

But my technique apparently sucks ass -- it generally looks like i cant get enough solder on all the pads to make good contact.

My success rate is like 5% - terrible.

I use a hot-air at 400C to get the top heatsink off (thermal adhesive)
I preheat the bottom - use a hotair at around 250C to pull the chip.
I have no problem getting the chip off nicely, and also removing the rest of the thermal adhesive.

From that point ive tried all various combos of fluxing the PCB pads and putting solder down, trying to flux and re-tin the IC pads, not using flux, etc.
It always looks "too dry" around the pads and I'm sure they aren't making contact correctly.

I'm not really sure what else to do - perhaps my solder and flux are not correct?
I am using leaded solder 60/40 Sn/Pb and Amtech VS-213-A-TF flux

Will send sats for good tips!

[1715356115]

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[1715356115]

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[mikeywith]

You need to use a tin tool in order to stick the chip , something like this.

What happens is that after you heat the solder on the chip to remove it and since it has already been heated the first time it was installed the solder is no longer good enough to make 100% contact so you need to re-do the tin/solder process,you have to use a liquid solder for this.

Place a bit of flux and drop that chip, make sure you position it perfectly and the flux will make it easier , then use something like a pick to push the chip down while heating it from the top.

[lightfoot]

QFN and chips like the Antminer ones are real pains in the rear to replace on a board. Using a preheater is an excellent idea, as is using lead/tin solder paste for the replacement as it flows a lot better and is a lower temp than ROHS.

I would say try cutting down the heat on your air gun to something like 360 on the re-solder. You don't need as much heat as when you're pulling them, also how much airflow are you using (sometimes a lower flow rate is better as it creates a cloud of heat over the chip instead of washing it with heated air).

For cleaning the pads on the board should be bright and shiny. I use 95% isopropyl alcohol and no lint swabs to clean them off. Make sure it's flat as a pancake, and get rid of any remaining heat sink glue on the board.

You might want to buy a few S9 chips new from Ebay just to see if the problem is bad chips. Maybe they are getting damaged on removal from the board and are thus duds.

Flux is always critical. I have found that zephlux is like nectar from the Gods: It's tacky without being sticky, holds components in place and when heated allows the solder and the component to "float" into final position. For removal I make sure to put Kestrel 951 (I think that's the number) liquid flux down first to help the solder melt cleanly.

Do you have a testing rig, or do you put heat sinks back on and test in an S9?

C