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Old 9th April 2013, 06:53 AM   #1
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Default SMD Parts and the DIYer

SMD parts require tooling not found on a "typical" tube/valve DIYer's bench. The soldering equipment we use rates to destroy the parts, before pigtail leads are attached in a satisfactory manner. OTOH, some useful items don't come in leaded versions. I've found myself wishing for leaded versions of parts, like this Schottky diode, on any number number of occasions.

How to escape from "Frustration City"? My thinking is to attach pre-tinned, solid, copper leads to desirable SMD parts with silver bearing, electrically conductive, epoxy. Please notice that curing time decreases and conductivity increases with the application of heat. The hot air guns we use with heat shrink tubing, set on the low setting, appear to be a good fit for the elevated temperature "requirement". Given the high cost and 2 year shelf life of the conductive cement, working on batches of parts that exhaust a given epoxy supply seems to be proper procedure.

Have at it, guys! Do my cogitations have merit?
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Old 9th April 2013, 07:57 AM   #2
tomchr is offline tomchr  United States
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Depends... If your workbench contains a half decent soldering iron like a Weller TCP or WTCP and you have a fine tip for it (I recommend a 1.6 mm chisel tip), then SMDs are actually not that bad to hand solder. I think a lot of the apprehension that people have stems from fear or intimidation and "I can't possibly do that" mind sets. And some of it is just lack of experience.

Here is my suggestion:
Make a prototype board that has a bunch of 1206 footprints. Solder some resistors onto those. Then do the same for 0805 and 0603 if you want to push it a bit. You'll probably have to run some traces away from the footprints to avoid lifting the pads. When you master that, move on to actual circuits.

Much of SMD soldering by hand comes down to tricks of the trade. Here are mine:
1) Flux is your friend. Get yourself a flux pen. Flux increases the surface tension and makes the solder wick to the pins and not make shorts between pins. This works particularly well if you have a board with solder mask (the green coating you see on my boards for example).
2) Use a fine tip soldering iron. I use a 1.6 mm chisel tip. I also have a 6.3 mm chisel tip for the tabs that are used on power components (TO-263 packages).
3) Use thin solder. Get some that's 0.5 mm in diameter. It really makes it easier to get the right amount of solder onto the joint.
4) Another friend is solder wick (aka desoldering braid). Get some fairly thin stuff - maybe 2-3 mm wide.
5) Get a pair of non-magnetic tweezers. Don't go cheap here. I think I paid about $40 for my Techni-Tool titanium tweezers. They're worth it!

For resistors, tin one pad, then place the resistor and hold it with tweezers while reheating the solder. Let the resistor sink into the solder, remove the soldering iron, allow to cool. Then solder the other pad. Go back and retouch or clean up with solder wick if necessary.

For ICs without tabs (like SO-8 packages), I normally tin pad 1 and use a technique similar to what I describe above. I solder the corner pins first, then the rest. If you get a solder bridge, clean it up with solder wick.
For bigger ICs like QFP packages, I solder the corner pins using a similar method and then solder the rest of the pins. It's rather hard to not get a solder bridge, so I often just put globs of solder on and clean it all up with solder wick after. Even after using the solder wick, there's usually enough solder left to from a good bond.
For power devices and regulator ICs with tabs like the LT3080 I use in my 21st Century Maida Regulator, I tin the thermal pad and the tab on the device first. Then using the 6.3 mm chisel tip, I heat the tab and the PCB footprint simultaneously and let the IC settle in the solder. Then I solder the pins. If the tab is not exposed - like on the LM22673 in my Universal Filament Regulator, I heat from the bottom of the board through the thermal vias. I have pictures of this process on the Universal Filament Regulator site (see my website below).

The key with all of this is to apply flux to the PCB footprint before soldering. It's not so critical with resistors, but for anything with closely spaced pins, it really helps out a lot. As does having a board with solder mask.

If your eyesight makes it hard to see the components, I suggest using either a dissecting microscope (5~10x magnification should do it) or a magnifying hood. They're actually not that expensive. I don't recommend the lamps with magnifying glasses. They often don't have enough magnification. For some, a pair of reading glasses may be enough to allow your eyes to focus on the components.
I find that I'm able to solder 0805 without magnification. I can do 0603 as well, but I really prefer to have a microscope available for that. Especially if the board goes out to a customer.

Hope this helps...

~Tom
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Last edited by tomchr; 9th April 2013 at 08:06 AM.
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Old 9th April 2013, 08:27 AM   #3
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Tom,

Thanks for the reply. What you said makes lots of sense, when working with PCBs. My ideas are oriented towards P2P construction. The Schottky diode I linked would be damned useful when bridge rectifying "120" VAC, with either 4X SS or 2X SS and a vacuum rectifier. Zero SS diode switching noise is a wonderful thing.

BTW, I do own a Weller temperature controlled soldering station and a grounded, cheapy, LOW wattage "Rat Shack" pencil. I remain very leery of parts without leads.
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Old 9th April 2013, 09:01 AM   #4
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You could make a very small rectifier board by etching, grinding, or cutting the copper from a single-sided blank. Leaving large area pads for soldering the SMDs and drilled holes for the connecting wires, or using cut component leads to solder it right onto the main board as a homemade module.
A clean board and flux ("Use it like your brother-in-law sells it," as the saying goes) is half the battle; just getting used to the new dimensions is most of the other half. The rest is just making a good fillet.
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Old 9th April 2013, 11:21 AM   #5
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I have to use a magnifier, but find the work not too difficult. Temp controlled iron with chisle point, fine solder, a wick, and a little patients goes a long way. Solder masks are a must, but that is from my experience so far. Only made a few prototype boards for SMD.
Cleaning the flux is an absolute must.
Just my 0.02.

I figure if I can do it anyone can
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Old 9th April 2013, 01:57 PM   #6
Magz is offline Magz  United States
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I use surface mount schottky bridges routinely in P2P construction. I simply flatten out the "gull wing" leads and solder them to wires I've previously mounted on perf board; said wires then make the needed connections in the circuit. I collect lead snipping from my leaded components in a little plastic ziplock bag and use those to make p2p connections.
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Old 9th April 2013, 02:08 PM   #7
Magz is offline Magz  United States
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For more complex smd parts like opamps I find the best solution is to stick the smd part to the board with a tiny piece of Blu-tac or mortite on the body (I mean TINY, jusy enough so it doesn't move) then flood the leads on with solder and wick off the excess. Works like a charm.
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Old 9th April 2013, 03:11 PM   #8
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A past roommate of mine who was in school to be an electronics engineer at the time (now does R&D at a well known consumer electronics company) would do surface mount small chips like a QFP-48 with a heatgun and solder paste, and would then use a fine tipped iron, fine wick, and a fine hobby knife type razor blade to clean up any excess, but he was pretty good at it and rarely had to do any retouching from what I remember. I also remember him reflowing a board he etched in a old frying pan on the stove once...seemed to work! I haven't tried his heatgun method (haven't needed to do small chips), but will be soon, so I may not be remembering something important about how he did it. Secure the board to something, and hold the chip in place with tweezers so the air doesn't blow it away, I think he would also use a dab of some fairly sticky flux to hold the chip if the solder paste itself wasn't enough.

Fiddly chips are probably best to put on a breakout board, many different packages are available online for hobbiest fairly cheap with solder mask, less tiny chips like to-252's and most surface mount opamps, resistors and caps can be done by hand with a soldering iron with a fine tip.

My hands aren't that steady and shake a bit when i try to do fine work so I have a block of high temperature plastic of some sort (I think it's teflon, it was an off-cut from a different engineer friends project, either way it's white, shiny, and my 25w iron doesn't melt it) with a notch filed in one side to support my soldering iron. I rest the thick metal body of the iron above the tip on it, about mid way up. I got the idea shooting with a rifle rest one day. If I can do surface mount chips this way pretty much anyone should be able to as well.

That diode would be easy to do with an iron in the method I've described above, again, secure your board to something, use tweezers, and solder paste makes it easy. Lead based solder melts at a lower temperature so I find it makes surface mount easier, and would probably be a good idea with the heat gun. I'm sure lead free would work fine too though.

I think I've seen clamping "sockets" like the ones used for computer CPU's for opamps and other similar surface mount components, these are an option if you want to be able to easily replace or change a chip, however I think they were pretty expensive and I'm not sure how available they are or for what packages.

Good luck! Surface mount really isn't as hard as it seems like it would be, it's way more DIY friendly than some would have you believe!
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Old 9th April 2013, 03:27 PM   #9
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by Eli Duttman View Post
SMD parts require tooling not found on a "typical" tube/valve DIYer's bench. The soldering equipment we use rates to destroy the parts, before pigtail leads are attached in a satisfactory manner. OTOH, some useful items don't come in leaded versions. I've found myself wishing for leaded versions of parts, like this Schottky diode, on any number number of occasions.

How to escape from "Frustration City"? My thinking is to attach pre-tinned, solid, copper leads to desirable SMD parts with silver bearing, electrically conductive, epoxy. Please notice that curing time decreases and conductivity increases with the application of heat. The hot air guns we use with heat shrink tubing, set on the low setting, appear to be a good fit for the elevated temperature "requirement". Given the high cost and 2 year shelf life of the conductive cement, working on batches of parts that exhaust a given epoxy supply seems to be proper procedure.

Have at it, guys! Do my cogitations have merit?
Eli,

I have never tried your method. My greatest worry would be leads breaking or you may not get a good electrical joint.

I do a lot of SMT hand soldered boards for my business. Typically I favor 0805 footprints and I do a lot of hand soldered fine pitch leaded ICs all the time. I use a pencil iron from Pace with a tiny hooked tip. The bent tip helps a lot because I can work at odd angles and I can present as much of the tip to the component as I need.

As stated before, flux is your friend. I use copious amounts and wash it with acetone.

I also use PC boards from Express PCB. They have a simple 4-layer CAD program for free that works extremely well. I do a lot of small run boards and use their production 4-layer service that costs about $110 for three 2.5" by 3.8" boards with solder mask.

You layout one 2.5" by 3.8" board any way you want, divide ground and power planes if you want, and subdivide the boards to get multiple boards out of one, if you want. Express PCB then makes three of those boards for that one price.

There are other services they offer, so check them out.

My point is that PCBs make life very easy and SMT doubly so if you choose to go that route. I like SMTs because you can cram parts together and reduce noise and board space. You can also put through-hole parts in there for a mixed topology board, which we do a lot.

Once you start doing SMT you will really not want to do much through hole work any more. It is just that good.

For the well heeled, Pace makes a killer solder/desolder station with a hot air reflow iron and a desoldering iron. It also can use solder tweezers to pull off SMT parts. It is model MBT 350. Expensive, but if you do a lot of soldering it is the cat's meow. I use the hot air reflow iron only for shrink tubing.

Last edited by Loren42; 9th April 2013 at 03:32 PM.
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Old 9th April 2013, 03:40 PM   #10
Loren42 is offline Loren42  United States
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Quote:
Originally Posted by Magz View Post
For more complex smd parts like opamps I find the best solution is to stick the smd part to the board with a tiny piece of Blu-tac or mortite on the body (I mean TINY, jusy enough so it doesn't move) then flood the leads on with solder and wick off the excess. Works like a charm.
If you apply a good bead of solder flux to the leads before soldering you can literally wet the solder tip and roll it along the IC legs.

The flux will automagically wick the solder along with the tip so all you need to do is wash the board in acetone or alcohol to remove the excess flux.

I routinely do .65mm pitch ICs this way without solder bridges or solder wick, which adds more heat stress to the part.
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