Soldering iron tips, how to solder SMD without ruining the PCB

Flashlight Modding and DIY Parts
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I want to get here tips from experienced people, also some how to do videos and other guide tips

You can solder all day on the boards without stripping pads if you solder with 280-295 degree Celsius and leaded solder,
what kills pads is too much heat, unregulated irons get easily to 400°C and more, they destroy the glue between PCB and copper

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generally soldering SMD with unregulated iron is a really bad idea, you have to be very fast so the pad does not overheat
better invest like 45$ for an iron or mini station with T12 tips or other Hakko clones

Station
HW version should be 2.1S
https://de.aliexpress.com/item/32837522724.html
newest revision
https://de.aliexpress.com/item/32950981884.html

v2.00 is quite cheaper but it has some flaws

Mobile
(needs a 19-24V PSU like Laptop ones, more voltage more power)
https://www.banggood.com/MINI-TS100-Digital-OLED-Programmable-Interface-DC-5525-Soldering-Iron-Station-Built-in-STM32-Chip-p-984214.html

T12 tips


pro:

- you have in each tip the heating element, so if it dies you need no expensive replacement than other stations have
con:

  • variation between tips in the temperature reading

preferred tip shapes for 0603 soldering:
BCF1, D16
for general soldering:
D24
for MCPCBs:
D52, C4

Pre tin pads and wires is a good solution, especially with unregulated, just keep the solder time as short as possible

The pads on my newer designs are reinforced with a via so a melted glue by too hot iron won’t lift it, then too much mechanical force removes the pad

To remove an unwanted bridge I use a tip which is flat on the front, so I can simply push the solder to one pad and the bridge is gone
using rosin core copper braid to remove unwanted solder bridges with an unregulated iron is a bad idea

This is the most effective Weller tip shape I use in 100% of the cases if not more heat is needed like on MCPCBs, you can solder even 0402s even if the tip seems gigantic compared to the resistor
The flat end is so much better to solder SMD, if you rotate it you have an area that easily makes contact with both ends of a 0603 resistor

To remove a resistor I usually add carefully some solder then flip the my tip by 180° so I can use the longer side melting both ends
too bad T12 tips are not available in such an angled design

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Flux and solder wire

A main reason why soldering can be hard is the quality of the solder wire or flux you use, usually flux helps to remove oxidation and also conducts a little heat

Quality solder wire is a key for low temperature soldering,
I did once the error to buy some cheap 0.3mm leaded from China but that stuff was the least shit did not solder at all at my usual 295°C
good solder wire is not cheap

Generally rosin core SN62Pb36Ag2 is one of the best compounds you can find

reflow soldering you need a flux that does not burn like rosin core
Amtech NC-559-ASM-UV is a good one,
but with many of them a good ventilation or solder steam filtering system is good

If you do a lot of soldering and want precise amounts of flux or different fluids like glue/thermal paste applies its best to get a proper dispensing solution

1 Thank
2

I took a 3x time lap of 3 different irons with IR camera,
I prepared the regulated with some heat shrinks so the thermal image reads right as I recently cleaned them from the burned stuff

2 regulated left and right and in the middle a very old unregulated I found
the unregulated needs far more time to heat up and finally exceeds 385°C my camera supports this is already way too hot
the real heat up of the regulated is shorter than in the video because of the heat shrink preparation
the main problem is the iron does not cool down at the tip soldering low mass objects

Pad soldering

Hardware

- 295°C Weller WSD81

  • Felder 0.5mm Sn62Pb36Ag2 with 3.5% flux (one with relative much rosin core flux, general use not SMD which has less flux %)

Preparations

- clean PCB with Alcohol and cotton swab

- twisting the wires end (helps to prevent splicing while soldering)

  • cleaning tip in sponge

1.

- pre tinning pad and wire

  • heating up pad and stick the wire end into it
  • same as 1. just adding extra flux (for example if you use a SMD solder wire with only 1% flux)
  • directly solder wire to the pad (not recommended but works fine with a solder wire with 2.5% or more flux)

in the video I look without any magnification to the soldering, just the camera records

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Some 0603 soldering with regulated iron

First the usual without adding flux at the beginning, the rosin core gets very nice results and perfectly tin first pad,
but 2. Pad is not fully soldered, even when flux added and more soldering time used

2. adding some SMD flux at the beginning the tinning of first pad is a bit slower

I use a relative aggressive form of getting the resistors off, I highly recommend this only when the left side is a solid copper plane that completely surrounds the pad, in very few cases that ripped a pad off with just s small trace connecting it

1 Thank
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reserved for tips of other people

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Corrosion on older soldering gear

I noticed on my Weller station that with the years the contact surface between tip and heating element gets corroded
Especially when I was often switching between tips it made it worse, I did fine sanding on the tips bottom a few times, now the copper is exposed and it degrades more quickly
some aluminum oxide heat paste should help fill the gaps but likely new planar metal on metal is better, just really tighten it to get as much Metal to metal contact as possible

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I highly suggest a solution where the tip and heating element are one piece
and the tip is plated with iron and chrome

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Usually if you got a decent tip with different coatings you can use it for many years without any degradation if using leaded solder
The hotter the iron runs the more and quickly oxidation builds up
Never leave regulated or especially unregulated irons longer times without enough solder on them as the iron oxidizes!

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Intelligent stations or irons use different techniques to get into sleep to avoid corrosion

- a motion sensor in the handle (can also wake up with no button press)

- the station notices for some time a constant use of heating power and it goes into idle later shuts off

  • timed simply goes after a time into sleep

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There are special mixtures to refresh an oxidized tip

A brass sponge helps to remove oxidation

never use mechanical things like sanding or filing on modern tips as you destroy the coatings
once the protective iron plating is gone the copper core will slowly be eaten away

1 Thank
5

Good idea!

No pun intended? :smiley:

My basic tips are that the tip needs to be clean when in use as dirt/oxidation will restrict heat flow, and covered by solder when not in use to prevent oxidation, so add solder to the tip before turning the iron off, or if the iron will be on but unused for more than 5 minutes or so.

You’ve mentioned leaded solder, the reason for using it is that it melts at a lower temperature than lead-free solder, hence keeping the overall heat applied to the PCB down. (I know you know but beginners might not.)

Using a damp sponge to clean a tip will reduce the temperature of the iron a little, so wait a couple of seconds for it to regain temperature or even better, use wound-wire cleaners (i don’t actually know what they’re called!) to clean solder off the tip.

If a tip is oxidised (looks a bit rusty) don’t scrape or file it off, this was ok with all copper tips as it revealed fresh copper but most modern tips are coated so you’ll end up scraaping the coating off and rendering the tip unusable.
Best way to clean a tip is to apply flux and then wipe clean, repeating until the oxidation is gone and the tip is shiny. If you don’t have flux you can use solder which contains flux for light oxidation, though this may feel like a waste of solder.

It’s also woth noting that a brand new tip should be tinned before first use, so wrap a little solder around the tip before heating up for the first time, the solder will melt, covering the tip, preventing intial oxidisation.

1 Thank
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I think you should also mention cleaning. (I see you added this but I will leave my comment)

Too high of heat causes another problem: your tip will oxidize right in front of your eyes and make bad heat transfer to solder. then it makes a novice think they need to set it hotter still or hold it on component longer than necessary

Your tip should be somewhat shiny with either no solder or fresh solder on it. The easiest way to get it clean is just to melt fresh solder on it then wipe it off with brass “sponge”. If you have an ancient tip that doesn’t get shiny after a few tries of this then it’s probably best to just replace it with more appropriate tip shape suggested above and do not overheat it.

7

I have been finding that some of the solders used on the main wire contacts with the mcpcb’s does not want to quickly melt. Some of this is due to the copper heat sink, but some is, I believe, due to the makeup of the solder used from the factory. I have found that just a tiny bit of solder on the tip really helps to melt the existing solder initially. After this, it will melt easily and quickly once nearly 600F is reached at the surface. Form mcpcb work I will typically run just a little hotter to get the solder work done more quickly, but to hot will damage the mcpcb.

8

I do this as well if I know it’s going to be stubborn. Alternatively, if there is already a lot of solder or tight working conditions where I might accidentally bridge something I don’t want by risking more solder spreading I will use tacky flux paste (not liquid kind, it’s worthless and evaporates right away):

Also, no clean just means “less cleaning”. You will still want to clean up the area when you are done with alcohol.

9

flux is game changer when soldering, you can never have too much flux

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You say that, but now everything is sticky. There’s flux everywhere, I’m crying, you’re crying, and I can pick up all my tools with one finger because they’re sticky!

I jest; flux is good, but don’t drown your parts. I did some production work microsoldering for a bit, and I used flux pretty liberally, but everything gradually got sticky… Fortunately, they had a solvent bath for the parts anyway, and I could just toss the tweezers in there once a week. My hands, though, could not go in that solvent bath, and trying to clean them with other methods (alcohol, liberal amounts of Dawn, Gojo, etc) gave me some severe dry skin issues.

That job was basically 100% microsoldering; while I don’t miss soldering that much, I definitely improved my skill… and I do miss the binocular microscope and JBC CD-S soldering station…

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After a good flux mess you always should use alcohol and clean the PCBs
I also wrote in first post that a proper dispensing solution helps put the flux in a very precise amount where you need it
also that stuff is not really healthy so a proper soldering steam sucking machine and probably gloves help

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I have used the Amtech NC-559-V2-TF Tacky Flux for about 2 years and its the best I have ever used. Cleans off very easy with rubbing alcohol.
You have to be careful when buying Amtech products, there’s alot of fakes out there. If you find it cheap there’s probably a good reason for the cheap price.
I buy it from here https://store.rossmanngroup.com/index.php/amtech-nc-559-v2-30-cc-16160.html
I bought the 30cc and dispensed part of it into a smaller (Tractor Supply) 10cc syringe and filed the needle blunt so I don’t stick myself. Makes squeezing out the right amount super easy with no mess or cap to stick on. It doesn’t come out at all unless forced.
I haven’t used the whole 10cc in the 2 years I have owned it but I dont solder everday either. Still more flux than I’ll probably use in this hobby.
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I total agree with Lexel with having quality solder, flux and iron. It really does make a huge difference in the quality and ease of soldering.
That’s the best soldering tip Lexel or me could ever give, the rest is basically practice.

13

Following with interest.

Can someone explain the differences between different kind of soldering irons, in particular regulated and unregulated ones?

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An unregulated soldering iron has the heater on constantly. They tend to take a long time to warm up and then run too hot making the tip dirty and possibly damaging the board or components.

Regulated ones have a temperature probe close to or in the tip and have an adjustable temperature setpoint. They are usually more powerful so they heat up faster and then the controller modulates the current to maintain a constant tip temperature.

15

:+1:

That’s very useful for me to know, thanks. I bought myself a soldering station two years ago without knowing what I was doing, and since then I’ve found the idea of soldering too daunting to approach it. But the more infos I have, the less scary the whole prospect seems, especially if I know what equipment and materials to use, and with as many pro tips as possible. It seems that I got the wrong kind of iron at the time, so I’m going to sell that again and get one of those that have been recommended by other forum members.

16

I took a 3x time lap of 3 different irons with IR camera,
I prepared the regulated with some heat shrinks so the thermal image reads right as I recently cleaned them from the burned stuff

2 regulated left and right and in the middle a very old unregulated I found
the unregulated needs far more time to heat up and finally exceeds 385°C my camera supports this is already way too hot
the real heat up of the regulated is shorter than in the video seen

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A thin layer of oxidized solder or burnt flux just kills heat transfer. Keeping the tip wet with fresh solder is important especially when using solder wick. Mcpcb’s are best done away from the heatsink with the biggest chisel or knife tip you can fit in there.

Sometimes traces connected to large copper traces suck a lot of heat away from the place you want to solder, ground planes are especially bad. Preheating the board with a heat gun or hot air station helps, making a blob of solder on a big ground pad and burying the solder iron tip in it for a while will also help spread heat through the board. Preheating should be done gently, the board’s fiberglass will burn if you get too aggressive.

Sometimes a component with a low maximum soldering temperature and multiple legs can be difficult because some of the traces are small and heat quickly while other traces traces are large and take a long time to heat up. Flooding the part with paste flux will help spread the heat around reducing thermal stress on the component and keeping air away from the traces preventing them from oxidizing. Make sure the flux is easily dissolved by isopropyl alcohol so cleaning up is easy.

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To anyone soldering, before you solder you joint, make sure to clean it well with isopropanol, or in the worst case scenario(or it’s just the solder pad is just full of old oxidized solder), just a very light touch of citric acid that is then to be washed away.

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11:11 sales are coming up so finding something should be easy. Youtube is a good resource, maybe try searching through some SGD Electronics videos and keeping an eye on the side thumbnails for anything interesting.

I have a Yihua combo hot air/iron soldering station, when the iron is in the station not being used for a couple minutes it will idle at a lower temperature and then quickly go back to the set temperature once its picked up. Really helps keep the tip in good shape. I like the little Yihua brass shaving ball tip cleaners that come in a little can with flux in the bottom of it. Wave the tip around in the brass and a quick stab into the flux cleans the tip instantly. Lastly find an assorted kit of the good Mechanic brand solder iron tips that fits the iron you buy. They heat up better and the tinned area is smaller so you don’t wind up with solder constantly running away from the point and creating a blob of solder on the shank waiting to run down and solder bridge everything. You’ll probably find yourself using one of the knife tips the most and saving the other tips for special applications.

I also have a KSGER with the T12 style tips. It’s a little quirky to set up when first using it but is in a different league performance wise. The cheap generic tips work ok but I had an end of one of the get stuck in the handle when changing tips one time, quite painful trying to get it out of there. My favorite tips for it are the Quicko XR series with the reduced tinned area.

20

Why do I always get a tail on the joint when I move the solder tip away from the contact?