Title says it all. I have a few SMD repairs to do, but don't have much to start with. Don't want to have to shell out big $ just to make a few repairs. I already have one of the Ebay 60 watt adjustable irons that had four tips included with it. One is cone shaped and comes to a point about the size of a pin. I'm guessing that's for SMD. Other than the original tip, the other four have never been used. What about solder, thickness and alloy as well as iron temperature setting? Thanks.
If you're not worried about destroying the removed part, then it doesn't really matter - the focus should be on not damaging the printed circuit hardware surfaces and tracking. Cut the legs off the part and desolder them carefilly, one at a time. Dress the pcb surface carefully and solder new parts, one leg at a time, starting with a single leg to position the part properly.
Use thin tin-lead flux-cored solder and a tip size that matches the job.
If you want to save the outgoing part, without hot air desoldering, you can use a 2mill nickel-steel shim (removed from the old stick- on security devices) fitted into an exacto knife handle to separate desoldered pins one at a time, as the shim advances underneath each spot-heated pin.
We use Chip-Qwik for removing SMDs using a regular soldering iron. Very handy when we don't want to dig out the SMD system for just one or two chips/devices.
As for soldering in place there are some nice flux pastes out there with powdered solder in them and you can use a regular soldering iron to install the SMD part.
Otherwise, some flux helps, and I use a #7 pencil tip on my old Weller station along with Kester 63/37 solder.
I suggest you break the piggy bank and get a decent hot air SMD rework station:
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Something around $50 to $70. You'll need an assortment of nozzles, tweezers, solder paste, liquid flux, acid brush, safety glasses, aluminum foil heat shield, vacuum desoldering pump, and whatever else I forgot. Practice removing and reinstalling parts on some junk PCB's before you attack your project. Just about everything made after 1990 will be RoHS solder (unleaded). It's difficult to determine which, so just suck up the excess solder after you've removed the components, and start over with fresh solder paste and flux. The aluminum foil is needed to prevent melting or burning adjacent components or hardware with the hot air. To prevent sparaying solder all over the PCB, launching the component, or melting nearby parts, keep the hot air flow as low as practical. There are plenty of videos on YouTube demonstrating how to use a hot air desoldering station.
Hopefullly your eBay 60 watt adjustable iron is temperature controlled. If not, I suggest you get a proper temperature controlled iron and assortment of tips. However, for SMD, I just use solder paste and flux to resolder the replacement component. I use a soldering iron only for physically large parts. The nice thing about SMD and solder paste is that you can roughly locate the position of the component. Once molten, surface tension will accurately position the component in the center of the pads.
Very good. I use some kapton tape instead of the foil to keep the heat away from other parts. Cover all the close parts and cut a hole where you want to remove the part. Get some very fine solder of the tin/lead type and one of the flux despensers that looks like the covid shot needle. Flux is your friend. Some of the desoldering braid comes in handy. I have one of the hot air stations like you show and it works well for the hobby.
One other thing that may be a deal breaker is a good stereo microscope. ONe like this is about the best buy for the money. I most often use the
10x, but I am 72 years old and started the SMD work about 10 years ago.
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The Amscope se400 for about $ 235.
Without the scope you can plan on spending around $ 100 to $ 150 for all the things you should need.
Well, not so good. As usual, I proofread my stuff after I post it. I should not have included a solder sucker. That's fine for old PCB boards with fat (1oz) and wide (0.1") traces. However, today's SMD PCB's use much less copper and narrower traces. Try to suck solder from a modern board, and the vacuum will suck the copper trace along with the solder. Best to leave the solder sucker out of the list.
Aluminum foil is cheaper, reflects the heat, bends around corners and conforms easily to odd shaped areas and parts. I have rolls of the really fine 0.021 lead/tin solder, but I never seem to use it. I've settled on Kester 44 rosin core 63/37 in 0.050 and 0.062.
I haven't had much luck using braid for SMD PCB's. Too much danger of overheating and destroying the pads. Braid is useful for connectors and cleaning up the mess when I use too much solder.
Old, but reliable:
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I have two others (but no photos).
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and one that was a prototype for a product that never was put in production. When I closed my office in late 2020, I dragged most everything home. I also emptied my Subaru, which was acting as a service "truck". So, I now have two or three of everything.
I'm 74 years ancient. The hands are still steady but the eyesight is becoming a problem.
Agreed. I have a small collection of assorted microscopes.
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For PCB work, I use an Olympus SZ30:
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Also, you might need a stand. This one weighs about 40 lbs:
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Look for a microscope that has as much working distance (between the objective lens and the work piece) as possible. Don't buy a biological microscope. Biological microscopes have all the fancy features that you don't need for electronics and all have a tiny working distances. If you are going to do much soldering under the microscope, plan on getting a fan to blow away the smoke or cleaning (or ruining) a few objective lenses including the one's on the turret that you're NOT using.
You'll also need a ring illuminator. Not having to deal with shadows is the main benefit. I have one of these:
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If I buy another one, I'll get one that emits more light or has more LED's. I also suggest using the microscope mirror light to illuminate the PCB from below, looking through the PCB. With luck, that will show broken traces, shorts, solder blobs, cracks etc.
Using a CMOS USB camera to see what I'm doing on a big LCD screen, was not as wonderful as I expected. It takes some practice to look at a screen, while soldering under a microscope. I need more practice. Still, if I were shopping for a microscope, I would get a trinocular. Be sure get a 0.5x reduction lens with the CMOS camera or the field of view will be about 1/2 of what's available. Similarly, if you find a monocular microscope with insufficient working distance, you can double the distance with a 0.5x Barlow lens.
Depends on what you're removing. If I'm removing a typical smd resistor or cap, I use the *large* knife edge tip. Using this, I can heat both ends at the same time. This also has a finer edge if you use the tip to clean up any sloppy soldering. As far as temp, it depends on the board. You would be better off preheating the board with a heat gun (hot, not scorched) and using a bit of liquid flux which reduces the time and temp you need to get the solder to flow. I have very fine solder but I generally use .032 for everything I solder (about 3/4 of my work is smd). I use 63/47 but remove all the original solder before soldering.
The best thing to do is find a smashed flat TV on the side of the road and develop your skills on those boards. You'll find the green boards (multi layer) require more heat than the brown phenolic power supply board does. Again, preheat and liquid flux.
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