Surface mount soldering: can anyone help with two chips?

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pythoncoder
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Surface mount soldering: can anyone help with two chips?

Post by pythoncoder » Thu Dec 26, 2019 4:20 pm

I'm developing a flash memory device driver for MicroPython. I ordered two S25FL256L chips but goofed: they are in WSON packages rather than the SOIC I intended. There is no way I can hand solder these but it seems a shame to discard two brand new chips

I have some of these breakouts. I'm hoping there's someone in the UK* who might solder the chips to the breakout boards for me.

*The cost of two-way postage rather rules out sending them abroad.
Peter Hinch

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Re: Surface mount soldering: can anyone help with two chips?

Post by stijn » Thu Dec 26, 2019 4:30 pm

pythoncoder wrote:
Thu Dec 26, 2019 4:20 pm
There is no way I can hand solder these
Have you considered trying? It's very doable on that pitch if your iron's tip is not overly large. Different techniques can be used. E.g. bit of solder on one pad. Grab component with pliers, hold in place pushing down, heat pad, release when component is flush. Rest of the pads is just heating pad/pin a bit and holding wire against it.

Edit: maybe you have 'diy repair shops' (nor sure what it's called in the UK) or so nearby, that's normally free.

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Re: Surface mount soldering: can anyone help with two chips?

Post by MostlyHarmless » Thu Dec 26, 2019 6:57 pm

@stijn is right, it can be done.

I remember that the Yuma TRX2 radio, I assembled once, had a few components that needed soldering like that. Not with 16 pads, but I don't think it makes much of a difference.

The trick is to have flux on the pads of the PCB and the component, use solder without rosin core and a very clean and pointy tip. As @stijn says get one point done and the component flush. The second point to solder would be diagonally opposite by just heating the PCB pad, then letting the solder flow in between the PCB and the component. The flux in place will do its magic. Repeat on all other pads.


Regards, Jan

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Re: Surface mount soldering: can anyone help with two chips?

Post by Roberthh » Thu Dec 26, 2019 7:51 pm

What coworkers and I did a few times is just to solder all pads without taking care of possible interconnections between adjacent pads. And then to remove the excessive solder with solder wick. Sounds strange, but worked.

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Re: Surface mount soldering: can anyone help with two chips?

Post by chrismas9 » Fri Dec 27, 2019 5:11 am

You could try adding solder bumps to the pads like a BFA. Try to get a lump of solder 1mm high on each pad of the WSON. Then tin the PCB pads with solder. Use liquid or paste flux on the pads and place the chip. With a very fine tip melt the solder bumps and that will flow into the pads and bond. They key to SMD soldering is pre-tinning the PCB and IC pads and using SMD flux.

You could also try SMD solder paste and hot air or toaster oven.

If you are not confident of any of these methods and height doesn't matter you can stand the chip on edge and make solder fillets on the bottom edge to 4 pads. Then use fine wire (eg one strand of hookup wire) to link the top row to the other pads.

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Re: Surface mount soldering: can anyone help with two chips?

Post by ghayne » Fri Dec 27, 2019 10:38 am

I have also used Roberhh's method with the solder wick and it worked a treat!

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Re: Surface mount soldering: can anyone help with two chips?

Post by pythoncoder » Sat Dec 28, 2019 9:19 am

OK, guys. I'll try again to DIY. Failing that I'll buy another pair of chips in SOIC packages.

The reason I find these packages a struggle are boring age-related problems of eyesight and fine motor control. I can clamp the board in place but trying to keep the chip steady while wearing two pairs of glasses and wielding an iron and solder has so far defeated me. Experiments with a hot air gun succeeded only in launching the chip into low earth orbit. ;)
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Re: Surface mount soldering: can anyone help with two chips?

Post by Planet9 » Sat Dec 28, 2019 10:39 am

Using low temp 60/40 solder might help.
I can supply you with a couple of S25FL128L in SOIC FOC if WSON doesn't work for you.

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Re: Surface mount soldering: can anyone help with two chips?

Post by mathieu » Sat Dec 28, 2019 10:48 am

Roberthh wrote:
Thu Dec 26, 2019 7:51 pm
What coworkers and I did a few times is just to solder all pads without taking care of possible interconnections between adjacent pads. And then to remove the excessive solder with solder wick. Sounds strange, but worked.
I second this suggestion, which in my experience works very well. I've done something similar a few times so far, with zero prior experience. Picture of my very first attempt can be seen at https://github.com/mdaeron/pybd-breakout, but since then I've improved significantly. Using low-temperature solder, it's very easy to heat with a hot stove or a hot air blower. For initial positioning (before heating) and final inspection (after wicking), I find it easier to work under a binocular microscope (mine is a kid's model, so nothing fancy).

Good luck!

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Re: Surface mount soldering: can anyone help with two chips?

Post by pythoncoder » Sat Dec 28, 2019 11:02 am

Planet9 wrote:
Sat Dec 28, 2019 10:39 am
...I can supply you with a couple of S25FL128L in SOIC FOC if WSON doesn't work for you.
Thanks for the offer but I already have S25FL128L chips in SOIC which are working. I want to prove my driver with the S25FL256L.
Peter Hinch

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