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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 23rd Nov 2020, 9:07 pm   #41
duncanlowe
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Default Re: SMD soldering

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Originally Posted by Steve G4WCS View Post
im struggling on the smallest parts in not getting too much solder on. May get a tub of solder paste and try it.
I'd try finer solder. That worked for me on a board someone designed for component size rather than ability to build manually. Biggest issue with that board is the crystal for the micro which is leadless so has to get solder under it.
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Old 23rd Nov 2020, 9:18 pm   #42
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Default Re: SMD soldering

Bench magnifiers run out of steam when you go smaller than 0805.... maybe 0603 if your eyesight is particularly good.

Keep your eyes peeled for a stereo microscope. They turn up from time to time. Low magnification and wider field are good. Stereo vision gives you a sense of depth and the servos for positioning your hands work a lot better

Solder not wetting suggests surface contamination and lack of flux. Flux really is the key to SMT soldering. You're working at a scale where surface tension in the solder will frustrate you. With a good flux, solder gets wetter or so it seems.

Solder paste is difficult to use and has a limited shelf life. I use small diameter flux-cored wire. Paste works best when you have a stainless stencil and a DEK screen printer in a production environment, for repair, it gets messy and difficult to control.

I've been designing, building and modifying SMT prototypes for about 36 years. Different people have different things that work for them, but you have to try variants until you find what works for you.

I microscope mount that can be swung over to give an oblique view when you want one is the one thing I wish I had. I'll make one someday.

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Old 23rd Nov 2020, 9:22 pm   #43
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Default Re: SMD soldering

For leadless components, I use wire solder and a Metcal to tin each pad on the board, making sure the flattened dome of solder on each pad is similar in volume and height. I then use a hot air gun to fit the part.... I had a JBC hot air gun at work. We tried a Weller one which kept burning out, and before that a Chinese blue one where the inner tube cracked and it kept blowing out sharp glass particles. I miss that JBC gun! In previous job, there was Pace hot air gun, but that needed a compressed air feed. Worked very well though.

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Old 24th Nov 2020, 2:30 pm   #44
knobtwiddler
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Default Re: SMD soldering

There are plenty of people who swear that they can build SMD designs by hand faster than when using TH components! After all, you don't have to snip the leads!
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Old 24th Nov 2020, 3:12 pm   #45
barrymagrec
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Default Re: SMD soldering

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Originally Posted by knobtwiddler View Post
There are plenty of people who swear that they can build SMD designs by hand faster than when using TH components! After all, you don't have to snip the leads!
Absolutely - or bend the leads or keep turning the board over to insert components then back to solder.
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Old 24th Nov 2020, 3:33 pm   #46
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Default Re: SMD soldering

Hi i now design things with smd for 1 off use prototyping boards no pcb to etch
i find with the 7 inch 1200mp lcd microscope on exxx around 35.00 pounds even with packed boards on some of the micro htts its easy to repair at component level. I used to dread changing things like the painter chip in philips colour tvs by todays standard this was a huge part.
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Old 24th Nov 2020, 5:10 pm   #47
merlinmaxwell
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Default Re: SMD soldering

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There are plenty of people who swear that they can build SMD designs by hand faster than when using TH components!
Me too, even quicker for home made boards, minimal holes to drill. And I also enjoy designing a PCB with no links maybe a ground plane if necessary, even that needs holes. I often use unused legs of components as pass throughs. All good fun and satisfying.
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Old 25th Nov 2020, 10:47 am   #48
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Default Re: SMD soldering

I agree Merlin..... but occasionally..end up with a trouble shooting scenario.. My Topband PA driver circuit required a 100R from base to ground....with 220 X 220 in the base bias..the transistor "went off its head"....found the 100R was infact 1K0 the 100R section of the stock had been contaminated, I tested over 200 X 100R. and found about 5% contamination. Trouble is..... I must now check the 1K0..of which there are about 500..
I use 0805 format of SMD's ....... The down side is the SMD inductors... most of which are not printed with values... thus unknowns are measured with my RF osc and counter.
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Old 29th Nov 2020, 9:51 am   #49
georgesgiralt
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Default Re: SMD soldering

Hello,
I'm a bit late on this subject, but...
I bought some SMD soldering practice boards (made in ... China, you guessed).
These are very cheap, and have various size SMD chips to practice on. As they are quite a number of them, you can acquire a proper technique and practice it.
I have started with this kind : https://nl.aliexpress.com/item/32812...archweb201603_
but there are a lot of different versions (some of them with multi pin challenging chips... ) and you will find them on all the usual suspects : Ebay;Banggood, Aliexpres, etc...
They helped me get proper technique and I was not afraid to fry one chip as they serve no purpose (the centre pad has LED on it and will flash if properly soldered and powered...)
Enjoy !
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