Smd soldering tips

Chat about pick and place machines, reflow ovens, assembly techniques and other SMT tips & trix

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stixman2364
 
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Smd soldering tips

Post by stixman2364 »

Hello all, I have tried just about every Smd soldering tip on the internet and none of them work. Just a blob of solder on all pins. Flux and solder wick doesn’t work. Using very little solder doesn’t work. Please help if you can. This is very sad for hobbyists as Smd doesn’t work well. It’s NOT easy as some say.

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dastels
 
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Re: Smd soldering tips

Post by dastels »

What iron do you have? I've had good success with a Hakko FX-888D and the Hakko SMT tip.

My approach: Load solder on the pads. Position the chip and while holding it in place remelt the solder to bond the chip to the pads. Use solderwick to pull odd excess solder, leaving only what connecting the pins & pads. I've built dozens of boards this way without problem. Caps, resistors, etc are a bit different: put solder on the pads, hold the component in place while melting solder on alternate pins to seat it. Clean up with wick as required. Tweezers are indispensable.

Dave

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T_Mo
 
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Re: Smd soldering tips

Post by T_Mo »

I've not heard anyone say that SMD parts are easy to handle.
I've seen a lot of rework done with a specialized hot air gun instead of a soldering iron.

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millercommamatt
 
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Re: Smd soldering tips

Post by millercommamatt »

For me, success came with having a clean <2mm chisel shaped iron tip, very small gauge flux-core solder, lots and lots of flux, and lots and lots of practice. Start with with big, chunky parts and move your way down in size as your skill improves. Dave Jones' videos on SMD soldering are a classic reference. You also have to accept that some stuff is too small to hand solder for most mortals. 0805 resistors are about as small as I'll attempt and success is not guaranteed at that size for me. To get good, you have to be willing to wreck some parts before you get a feel for it. Finding a coach will get you productive the fastest. I spend a lot of time with some learn-to-solder kits from eBay where you make random light up doodads.

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stixman2364
 
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Re: Smd soldering tips

Post by stixman2364 »

Thank you all very much for your help.

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Timeline
 
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Re: Smd soldering tips

Post by Timeline »

I will just add that I have found many of the "no clean" fluxes to be rather weak and prefer the full strength "rosin activated" fluxes and solder. I then just clean the flux with 99% Isopropyl Alcohol and a flex brush like these https://www.acehardware.com/departments ... es/4695128 with the bristles cut down to about half their length. Those brushes last forever.

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adafruit_support_mike
 
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Re: Smd soldering tips

Post by adafruit_support_mike »

I also use a Hakko 888 and my favorite tip is the hoof type:

https://www.adafruit.com/product/1248

Small tips have relatively low thermal mass, so you have to set the iron hotter to make the working end hot enough to melt solder. They have less surface area, so they hold less flux, and the flux burns off faster at higher temperatures. Then you get more oxidation of the solder on the tip. Overall, I tend to get less working time between cleanings, and have to work harder to keep the tip clean and freshly tinned so it will melt solder when I want it to.

The hoof is pretty massive compared to other small-point tips, so it holds temperature well. It holds a good coat of solder and enough flux to keep it clean for 30 seconds or so. I find it easy to clean and re-tin, and the oval tip has angles that fit into surprisingly tight spaces.

Timeline wrote: Wed Jun 26, 2024 11:03 am I will just add that I have found many of the "no clean" fluxes to be rather weak and prefer the full strength "rosin activated" fluxes and solder.
Technical note: 'rosin' and 'activated' are separate ideas. The meaning is 'rosin based flux with additional activators', not 'flux activated by rosin'.

And to clear up the jargon, 'active' means 'acid'. Acids dissolve contaminants on the surface of the metal you want to solder. They also keep the molten solder clean by dissolving any lead/tin oxides that forms in contact with the air. Those oxides break up into powder and mix into the molten metal, making it pasty. If your solder starts to behave that way, it's been hot without a flux layer for too long. You'll need another dose of flux to clean it up.

Rosin is a collection of organic acids that don't do much at room temperature, but get strong enough to eat thin layers of copper oxide at soldering temperatures. It isn't strong enough to cut serious corrosion, or oxides that form a chemically inert 'passivation layer' like silver oxide. For those, you need a stronger acid.

Plumbing solder contains zinc chloride, which reacts with hydrogen in the air to make hydrochloric acid. HCl will eat almost anything, including the base metal underneath any contaminants.. if it can't cut through, it goes under. The problem is that the acid doesn't go away, and keeps attacking the metal at room temperature.

The term 'activated solder' generally means zinc chloride. Don't use it for electronics, or anywhere near your electronics bench. HCl never evaporates, but it can dissolve in water vapor and migrate like a gas. You end up with a metal-corroding region that can last for years.

For electronics fluxes that need a bit more kick than just rosin, we use 'mild activators' that can cut a passivation layer but aren't as destructive as HCl. Citric acid and succinic acid are two of the more common ones, and both get quite nasty at soldering temperatures. Don't hunch over them when they get hot.

Fluxes also help the soldering process by floating on top of the molten solder, creating a barrier that keeps oxygen away from the metal. Boric acid does that extremely well, to the point that it forms a glassy layer that's hard to remove once it cools down again. Materials that behave that way are called 'no wash' fluxes because the residue forms a permanent protective layer.

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