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Old 3rd Nov 2020, 10:03 pm   #1
Steve G4WCS
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Default SMD soldering

about to commence construction of a G4DDK 23cm preamplifier, now its evening indoor projects weather. Smallest devices are 0603 smd. Ive ordered a 0.3mm tip for my soldering station but I feel this will still be too big. Do I recall someone on here recommending a reasonably priced 12 volt tiny iron ?

Also for smd rework, I usually tin the pad with SMART (silver loaded) solder, then rework flux and hold the device down with tweezers, but I feel for new assembly silver loaded solder paste would be more suitable, provided I can put down the tiny dots required. Again any recommends or tips gratefully accepted.

Wish me luck
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Old 3rd Nov 2020, 10:12 pm   #2
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Default Re: SMD soldering

Standard 60/40 solder should be fine and use your liquid flux to get a nice reflow. 0.3mm tip will be ok, a good magnifier and plenty of light help a lot too. Tin one pad on the board then slide component into position then solder up the other leg(s) and tidy up with flux as required. A spool of decent quality desolder wick will pay for itself - SMT takes a bit of getting used to and everyone has their own methods.

Kev
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Old 3rd Nov 2020, 10:37 pm   #3
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Default Re: SMD soldering

Quote:
Originally Posted by Outrun_uk View Post
Standard 60/40 solder should be fine and use your liquid flux to get a nice reflow. 0.3mm tip will be ok, a good magnifier and plenty of light help a lot too. Tin one pad on the board then slide component into position then solder up the other leg(s) and tidy up with flux as required. A spool of decent quality desolder wick will pay for itself - SMT takes a bit of getting used to and everyone has their own methods.

Kev
All good advice, I'm an ex camera engineer and did loads of smd work, .2 mm solder is recommended as is a good liquid flux syringe, luxuries are a metcal iron and a stereoscopic microscope, a useful trick is to solder the parts one side first but a little offset so there's a bit more solder pad on the other side to get the iron into as sometimes the solder stubbornly refuses to flow both the component and the pad simultaneously, then some alcohol to clean up excess residue, goes without saying to be as speedy as possible to avoid damage to parts and print.
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Old 3rd Nov 2020, 11:39 pm   #4
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Default Re: SMD soldering

Each to their own, personally I used to a 3.5mm tip combined with liquid re-work flux and decent fine solderwick, I found the bigger tip kept better heat when using the solder ball rolling technique, I never tried to solder the pins individually.
Liquid flux and a Weller Pyropen hot air tool was used to finish off, after cleaning with a cotton bud and IPA afterwards you couldn't tell the chip had been replaced.
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Old 4th Nov 2020, 12:14 am   #5
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Default Re: SMD soldering

Oh! and a pair of reverse tweezers are brilliant for replacing/placing two/three legged components, well worth getting a pair.
things became much more difficult with the advent of leadfree solder though and BGA devices, the board you have shown so far should present few difficulties as the pin spacings look quite wide compared to the stuff I was reworking.
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Old 4th Nov 2020, 12:41 am   #6
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Default Re: SMD soldering

Reverse tweezers act to limit the squeezing force on the part and thus the impetus imparted when the inevitable tiddly winking happens.

Soldering iron bits need pretty fine points, you'd think. But slender bits are lousy at transporting heat right to the tip and your soldering quality suffers. Metcals ease this with the heater very close to the business end. You can help by choosing a stubbier bit, or even learn to solder with a wider bit. I use a 3.2mm screwdriver shaped one most of the time. I solder a few IC leads at once and rely on surface tension.

There are several ways. You'll play about a bit before you get comfortable and find out what works for you.

A hot air station is a good ancillary to a soldering iron, but not a replacement. The firm bought a chinese cheapie which worked but the tube inside started breaking up and you never knew when the next bit of broken glass would be blown out. A weller one was disastrous and kept burning out elements. A JBC one has been far better.

The best hot air station I've ever used was by Pace but it needed an air line to supply compressed air.

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Old 4th Nov 2020, 1:20 am   #7
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Default Re: SMD soldering

Depending on what I was doing, whether replacing or brand new chips etc...
I would either remove the chip/component first by whatever method you prefer.
Then either clean up the pads with a fibre pencil and/or soldermop +IPA (depending if I was replacing or placing a device) if it was say a 128 pin chip the size of a stamp!, then after lining said device up in both axis, tag opposite diagonal pins with solder, then after coating with plenty of rework liquid flux 'splat' one side in after tilting the board trying to keep the solder ball running down one side of said chip, usually only the last three or four pins would be bridged, do the same again for the other three sides, the bridged pins can be cleaned up of bridges with the solder mop, clean again with IPA and a cotton bud, put some more rework flux on all four sides and then reflow with the hot air tool, finally clean up again with IPA and inspect with a magnifier to ensure no bridged pins.
This is actually a lot easier to do with practice than it is to explain, you get a 'knack' for this with practice.

Cleanliness of the soldered joints are paramount, plenty of rework flux helps a lot, good quality solder too. A large tip is always better ( ) more heat for a shorter duration is definitely the way to go, this may be somewhat counterintuitive but I think the last tips I used might have been even 4.5mm (for an Antex XS25) and this was used for replacing painter chips on the Philips A10 (of which I replaced dozens) which had about half the pitch (spacing) of pins of the devices you propose to use.
g
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Old 4th Nov 2020, 2:42 am   #8
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Default Re: SMD soldering

I found a Quick 861DW hot air station from Kaisertech invaluable for SMD stuff. The last project called for 0402 passives and had some fairly tightly packed devices which would have been nigh on impossible to do with an iron as the slightest touch can move them. I applied solder paste (standard RS 60/40 stuff) using a plastic cocktail stick rather than the syringe needle dispenser as it seemed easier to apply that way.
A few components needed removing and replacing for performance tweaks, and again the hot air station and a good pair of tweezers made it fairly easy to do so; excess solder was removed using desolder braid and an ordinary iron before reapplying a little solder paste and placing the new component.
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Old 5th Nov 2020, 3:47 pm   #9
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Default Re: SMD soldering

thanks for the useful replies. was wondering whether one of those portasol gas irons with a hot air (gas) nozzle could be used for hot air rework
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Old 5th Nov 2020, 4:11 pm   #10
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Default Re: SMD soldering

The temperature of the hot gas is a lot too uncontrolled. Items of small thermal mass can flash up to damaging temperatures while free from the heatsinking provided by a board.

David
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Old 5th Nov 2020, 4:21 pm   #11
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Default Re: SMD soldering

Hi practice practice is the most usefull , lots of dud hard drives etc going for nothing practice taking parts off and puting back on after a time 0402 no problem to take off and put back on . On a new board its simpler main thing is line up part with pads this is more important with multy pin parts ie ics with a small pin spacing most of all have conferdance you can do it hope this helps Mick should have said work in a uncluttered clean space

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Old 5th Nov 2020, 6:31 pm   #12
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Default Re: SMD soldering

Since this is a brand new board with clean pads and nothing needing taking off first, I’d suggest how we do it for small production runs of PCB’s at work, we put solder paste on the pads first, place most of the components, bake the PCB in an oven at 125 degrees for 10 mins, then stick it on a hot plate (one that is meant for soldering!) at about 260 until the solder flows. The baking stage is just to stop the solder paste spitting and leaving solder balls everywhere.

Not sure how much the hot plates are, the ones at work are Weller ones, so probably not cheap!

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Old 5th Nov 2020, 11:23 pm   #13
60 oldjohn
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Default Re: SMD soldering

Hi Steve, I have these practice boards and a few mixed smd FOC , Please PM me with your address me if you would like me to send you one and a few mixed parts. Measures 33cm x 3.5mm

I bought a Hot Plate from China similar to this, they do seem to have gone up in price in the last 12months.

OK link will not work. It's a 946c hotplate on Ebay.
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Old 5th Nov 2020, 11:33 pm   #14
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Default Re: SMD soldering

I use an old Morphy Richards smoothing iron for reflow. Clamped in a vice hot side up.
 
Old 8th Nov 2020, 3:17 pm   #15
Steve G4WCS
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Default Re: SMD soldering

Quote:
Originally Posted by 60 oldjohn View Post
Hi Steve, I have these practice boards and a few mixed smd FOC , Please PM me with your address me if you would like me to send you one and a few mixed parts. Measures 33cm x 3.5mm

I bought a Hot Plate from China similar to this, they do seem to have gone up in price in the last 12months.

OK link will not work. It's a 946c hotplate on Ebay.

Thank you, very kind PM SENT
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Old 8th Nov 2020, 3:46 pm   #16
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Default Re: SMD soldering

Practice, practice, practice, I started with SMD/SMT about 30 years ago, then (at the tender age of 30 ish) thought 0805 and SOT23 where weeny and hard to do. Now I have no problem with 0402 and 1/2mm pitch ICs by hand. The only problem I have is seeing the darned things, I have a selection of Poundland reading glasses and use them in series (hey six eyes) to get the right magnification. Use flux, get a bottle and a small paint brush, stick the bottle to a heavy base to stop it falling over, a bench covered in slow drying sticky stuff ruins you day.

The whole thing is easier with leaded 60/40 solder but not too bad with the modern unleaded stuff, you just need more flux.
 
Old 8th Nov 2020, 5:45 pm   #17
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Quote:
Originally Posted by merlinmaxwell View Post
Use flux, get a bottle and a small paint brush, stick the bottle to a heavy base to stop it falling over, a bench covered in slow drying sticky stuff ruins you day.
Flux and Brasso do make a mess, I decant mine into the old original containers, fill only enough so that when laid on its side nothing comes out, of course if I'm clumsy enough to knock it onto the the floor then I can expect a mess.

As for finding SMD, I vacuum the carpet before (plain beige colour) I start soldering. Makes life a lot easier when the little blighters start jumping like fleas. Oh and remember to give yourself a good shaking before leaving the room, if that missing transistor is stuck in your clothing once outside it will never be seen again!

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Old 8th Nov 2020, 6:34 pm   #18
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Default Re: SMD soldering

On microwave boards, like that one Sam's designed, you have multiple stitches going to groundplane. Plane connections will be hard, without thermal relief.

You may decide on a narrow tip for 0402s but you'll need something meatier with better thermal conductivity to get enough heat into grounded pads to get the solder to flow and give a proper wet joint..

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Old 8th Nov 2020, 10:04 pm   #19
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Default Re: SMD soldering

Lots of good advice already... in addition here's a few things that can go wrong.

As already mentioned, it's very easy to lose the parts especially if you pick them up with tweezers or try and press on them when they are on the PCB. They can ping across the room never to be seen again. My advice would be to only use the tweezers to nudge parts into position if you have only one of each part. Even then it is possible to ping the parts a long way if the SMD part isn't moved smoothly and slowly.

Try not to flex the PCB once you have parts on the PCB. SMD caps are especially prone to generating internal cracks and this is generally worse for long thin packages like 1206. 0603 is generally more robust but they can still break especially if the cap is a dc blocking cap near an RF connector at the PCB edge. Even the act of connecting coax to an SMA PCB edge connector can crack a nearby SMD cap leading to confusingly intermittent gain and passband performance. If your PCB is 1.5mm thick then this issue is less significant but if it is just 0.8mm thick then flex damage can be a real problem even with a tiny amount of PCB flexing.

If you build it with a soldering iron then it is possible to damage the components through thermal stress, especially if you try and straighten any parts that settle at a wonky angle. If you try to move a part that is already soldered at both ends then this is asking for trouble if you are using a single iron to swap back and forth across the part whilst trying to nudge it straight at the same time. One option is to use an iron with a double tip or to use two irons at the same time to heat both ends of the part. Of course, it's generally much better to use a hot air reflow pencil for stuff like this as it puts much less stress on the part.

SMD caps generally don't have a part code stamped on them so make sure you can't get in a muddle over the component value. Don't leave any excess 0603 caps lying about near your work area because if/when you do ping an SMD cap off the PCB you can easily mistake it for another loose cap that has a different value. Keep the work area clean and free of random SMD caps.

It's easy to create solder splash shorts under SMD components so this is one area where you need lots of practice. Mick's suggestion to practise with the SMD parts on a PCB from a dead HDD is a very good one.

Get some decent skinny solder as already mentioned. I have 0.4mm, 0.5mm and 0.7mm solder for SMD stuff although I really should also buy something finer.

A decent stereo microscope with a decent cold light is very rewarding to use for work like this especially if it has a zoom function. I bought an old Zeiss stereo microscope quite cheaply many years ago and it is one of the best additions to my workroom. The microscope is so good I rarely solder any SMD parts without it even though I don't need reading glasses to see up close. A decent magnifier would be a cheaper alternative although I find that they can introduce some optical distortion and it is harder to judge fine distances and this can be tiring.

Quote:
was wondering whether one of those portasol gas irons with a hot air (gas) nozzle could be used for hot air rework
I have a hot air reflow station here and I also have a portable Weller Pyropen (hot air) that can be used for SMD work. However, I rarely use the Pyropen. It is quite a scary (hissy!) and aggressive thing to use so I wouldn't recommend it. I generally tend to work on small PCBs like your LNA so I tend to be lazy and use a regular soldering iron.
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Old 21st Nov 2020, 4:24 pm   #20
Steve G4WCS
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Default Re: SMD soldering

Thanks to 60 oldjohn I have a board and parts to practice on. Spent the day assembling my armoury and dug out and cleaned my illuminated magnifier
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