How to replace stepper controler on Duet

Hello everybody

I have burned the extruder stepper controler and will now replace it with one I bought.


But I do not know how to get the old of the PCB .

Are there any good suggestions

jan

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XB70

It certainly can be done, for example, with hot air from a decorator's adjustable heat gun. The tricky bit is not displacing surrounding components and not scorching everything in sight. Before now I've used High-temperature Silicone (gasket grade silicone) as a temporary mask and fixant in a ring around an IC I wanted to replace using hot air:

[www.toolstation.com]


Leave it for as long as you can for it to cure (around two days) but peel it off as soon as you're done replacing the IC.

Alternatively, I've seen the suggestion that it's possible to use sand on a hot-plate to contact only the underside of the PCB where the IC is. Some sort of insulating support for the corners of the PCB would help. I guess this could be done using domestic kitchen equipment - though I've not tried it myself

Either way, it's a good idea to practice on scrap circuit boards to establish the best compromise between temperature and time taken for the heat to build up to the melting point of the solder. As usual, flux can help to aid thermal contact and get things moving.

What you don't want to do is use any mechanical force (e.g. snipping the leads or levering off the IC) otherwise the PCB traces may lift and then it's curtains for the board. When it's ready the IC will slide off.

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RS Components Reprap Ormerod No. 481

Whereabouts are you? There might be someone local with the proper kit?

Best way IMV is on a proper hotplate, with an air pencil to push the device pads up to the correct temperature.

You can do it with just a small hot air gun, preferably with a reducing nozzle.

I'd start with a fresh blade in the scalpel, cut each of the legs at the device body. Then remove the legs from the pcb with small soldering iron. (Sounds bad but I've never broken a pad doing this - use the tip of a rounded blade, and slice vertically downwards)
That will leave you with only the heat pad to deal with, and reduce the chance of lifting a small pcb pad as you work.

I often replace A4988 (28pin QFN package) on a 6 layer pcb with little thermal relief - it's do-able with practice, but never easy.

Edited 1 time(s). Last edit at 03/22/2014 07:23PM by epninety.

I'd use a hot air rework station or a hot air torch (e.g from Iroda) to remove the chip. Then remove excess solder using solder wick.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Try this [www.zeph.com] or similar ie. Chip quick alloy.

Just add the alloy onto the pads with soldering iron then suck it out with any method until it come out of the pads

Thanks for all your good suggestions. I try my way on old circuit

@epninety. I live in Denmark.

@Chaisaeng. I have ordre "SMD1 REMOVAL KIT, SMD" from chip quik

jan

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XB70

Guess I'm a bit too far away for me and my Metcals to help you out then Jan

I haven't studied the pcb design but there's one other approach that might help you get the device off without damage....

Underneath the device is the thermal pad, which you cant get to directly with a soldering iron. It should have vias through the board to carry heat into the ground plane.
If you scrape the solder resist on the opposite side of the board, then add, instead of removing solder, the solder fills the vias and carries the heat through the board.
Keep the added solder molten with a soldering iron, then with luck it only takes gentle heating from above with a hot air gun until you can lift the chip.
It reduces the risk of damaging the board or removing extra components with the hot air, and if it doesnt work, all you've done is scrape a small patch of solder resist.

You will need to cut the device legs off as I suggested above before trying this.

Dave

Quote
epninety
I'd start with a fresh blade in the scalpel, cut each of the legs at the device body. Then remove the legs from the pcb with small soldering iron. (Sounds bad but I've never broken a pad doing this - use the tip of a rounded blade, and slice vertically downwards)

No disrespect but I personally I think this is just too risky. The levering action as the leg parts company with the chip puts a lifting force on the pad. I used to remove small-outlne packs with 0.05" leads this way but I think I was getting away with it because the wider tracks typically had greater adhesion. As soon as I started doing it on packages with 0.5mm spaced leads I started ruining PCB's so switched to hot air removal.

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RS Components Reprap Ormerod No. 481

Er,sorry Edit! Wrong picture posted a moment ago.

This is the photo I should have posted showing the first step in removing the ARM chip from a Duet using silicone mask



The metal bits are there to contain the hot air (there's already enough of that around me)

Edited 3 time(s). Last edit at 03/23/2014 06:49AM by Radian.

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RS Components Reprap Ormerod No. 481

Quote
Radian
No disrespect but I personally I think this is just too risky. The levering action as the leg parts company with the chip puts a lifting force on the pad. I used to remove small-outlne packs with 0.05" leads this way but I think I was getting away with it because the wider tracks typically had greater adhesion. As soon as I started doing it on packages with 0.5mm spaced leads I started ruining PCB's so switched to hot air removal.

No problem, everyone has their own preferred techniques and tricks. I've been designing, building and reworking SMD boards for a living for 20+ years and I'm still learning
The guys in China reballing BGA chips by hand are just mindblowing (http://dangerousprototypes.com/2014/03/13/bga-chips-remove-reball-replace-the-easy-way/)
Up to now, I've been assuming that my duff BGA boards are just scrap, but I might find some time to experiment...

I regularly do this with LQFP144 packages with 0.5mm spacing simply to protect the pads from ripping. If you can get the board onto a proper rework bench, preheat and air pencil, or if you use a wider nozzle heat gun with decent temperature control, then it's not necessary. Sometimes that's not possible or desirable, and alternative techniques are necessary. Fresh from the packet scalpel blade is a given.

Recently I've been removing and replacing 0.4mm pitch 30 way micro-coax connectors using just this technique, again, without an issue.

I like the silicone technique BTW. It would have to be a very precious board for me to stop development work for 2 days, but there's always an exception, and a very useful option to have in reserve. More importantly, a time delay is much less of an issue for a hobbyist board.

Dave