Soldering Principles Chemistry and Physics: Helping a Rusty Newbie Solder

Thread Starter

Tentmaker

Joined Feb 16, 2019
2
Hello! This is my first post.

Summary:
Had questions about soldering regarding the chemistry and physics.

Background:
Used a Canadian Tire Soldering iron for past hobby projects and fixes. Threw it out after I bought this cheap soldering iron kit (60W, analog dial for varrying temperature) on Amazon for 40 bucks (CAD)... (Maybe that was a mistake in hindsight) To add insult to injury, I ended up finding the same one on Aliexpress for about half the price.

Now, bad decisions aside, I've soldered a few things and doodads over my relatively short life as I've always been a computer enthusiast since I was a child and do plan to professionally consult in electronics+programming. But, regarding practice: I haven't done it in a long while and forgot some of the details I once learned. Currently, am struggling with basic soldering... Trying to remove and replace an HDMI female connector on a little buddies PS4 mobo. Simply tried to wick up solder on pins and soldered mounts. The result: Black residue (there's some conformal coating on the PCB or something? Comes off with isopropyl alcohol). Not so pretty joints. *lets out big sigh of disappointment*

And, I am struggling though in the past I've had no problem with my hobby electronic dabblings like this (albeit the components or wires were a little larger)... So, now, after the set backs and frustration and disappointment over such a simple thing, I am wondering about the science behind it to guide how I should solder. So, without further adieu, on to the question:

Question:
Can you solder too hot? Anyone have tips (no pun intended)? Is it me? Is it my iron?

Post-question comments:
I've googled it and it seems like no one online on forums and instructional videos have said that there is a "too hot". They actually state the opposite. Someone who "taught this for years" said, "the hotter the better". And, most people who I saw comment on soldering temps have said the hotter the better (based on their experience).

But, my issue, then, is this: rates of oxidation. If my soldering iron tip oxides more rapidly at an unneccesarily high temperature (simply because rate of reaction of oxidation increases with increasing temperature as seen by blackening residue on soldering iron tip and neck), that will create an oxide layer which is not good for bonding and, (maybe insignificantly) reduce heat transfer. But, based on my understanding, it doesn't stop there: if I heat up my workpiece with a overly hot iron, I vaporize the flux, and, though it reduces and removes oxides from work-piece surface once heated, the surface may oxidize again rapidly due to heating (now, this may be true, but is this significant if soldering quickly enough?).

Also, I had this old piece of copper de-soldering wick in my kit... The capillary action and "removing" action doesn't seem so good? In the past, I would flux the wick and it would help if memory serves... But, this time I didn't... And, maybe my sweaty hands get on the braid and effect the wicking action... Do people wear gloves for this?

And, in reading these thoughts, you probably get how I do things: I'm a "Theory drives practice" kinda person... So, help on this matter would be sincerely appreciated as my practice is lacking and I want to make sure I understand the theory...

Thanks for reading and your thoughts! All friendly tips and comments are appreciated! :)
 

jpanhalt

Joined Jan 18, 2008
9,050
Welcome to AAC.

You are correct that a minimum temperature is usually given, but a maximum is not. For example, Weller gives a desirable tip temperature of 700° to 800°F for solder that melts about 400° or less (https://www.astro.umd.edu/~harris/docs/WellerSoldering.pdf ).

A hotter temperature can cause more rapid degradation of the soldering iron tip or increase likelihood of damage to parts. So, there are good reasons not to do that.

But is there really a temperature that is "too hot" to work. I believe there is. If you try to flame solder, you will find that at some point, the flux boils away, the surfaces oxidizes, and the solder doesn't stick. It is not often that you flame solder in electronics, but you do in plumbing. Also, if you ever try silver soldering with much higher melting alloys, you do need to watch that you do not overheat the parts (e.g., stainless steel is harder to silver solder when it is red hot). Again, that is not that the solder won't melt, but that the flux boils off and oxidation takes over, and the solder just balls up and doesn't flow out. As for what those too high temperatures are, I cannot give a number.
 
Some nut case decided to get rid of lead and the nice 60/40 and 63/37 alloys. The motherboard is multi-layered with plated-thru holes. What you find is that DC jacks and other connectors on laptops are on daughter cards.

MY very first SMT solder job was to replace a CPU in a car radio. Not fun, but it went well. I cut the pins, then removal was easy.
Soldering used 63/37 which melts and solidifies at the same temperature. So, you tack the corners and drag the solder over the pins while the part is upside down. Then look for and remove the shorts.

If you can cut the pins, cut them.

Chip-quick has an alloy that when mixed with the high temperature ROHS solder, it lowers the melting temperature which is a good thing. Never used the stuff yet, but it's a good idea.

vacuum de-soldering with a stand-alone tool is a good bet.

Soldering. I've done all sorts of soldering from pure Indium to silver solder including plumbing.

Plumbing, you can do in one of two ways. "Tin" both parts and then solder or put the pipes together and solder. No exactly. The surface needs to be clean and fluxed. Your "testing" for the correct temperature by "trying" to solder at the joint. With practice, you know when to let the solder at it.

I did a water heater replacement with a guy at work, so it was used as a training session. The deal was, I'll do the tough joints and you can do the easy ones. By tough, it meant if they leaked they would be difficult to fix. My training was successful.

The right everything matters. A clean surface really matters.

De-soldering can also mean adding new solder to partially removed solder, so it can all be sucked out at once. Don;t apply solder to the tip. You apply solder to the work and heat to the work.

Old days: Start with a clean pad. Use solder with built in flux. Place component in hole and wedge lead with iron and apply solder on the other side of the component lead while heating the pad and lead simultaneously.

If you think soldering is hard, try sealing off an quartz tube so that it's under vacuum when your done.
 

crutschow

Joined Mar 14, 2008
24,709
Too high a temperature is bad as it can lead to damage to the parts (especially semiconductors) and to a PC board.
You want the iron hot enough to rapidly heat the device being soldered to a good soldering temperature the flows the solder around he join, but no higher.
The Someone who "taught this for years" said, "the hotter the better" has been teaching incorrectly.
If not, you would use a red hot iron which obviously wouldn't work well.
For small electronic parts a small iron with a temperature of 350-400°C is often used.

Another common mistake is using too much solder on the joint.
You want enough to just wet the joint, but not so much as to hide it with a blob of solder.
You always want to be able to see that the solder has wetted both parts of the joint. Otherwise there's a chance of a cold joint.
A good joint will be shiny with all parts obviously wetted.
For small joints and fine pitch IC leads, you should use a small core solder size (something like 22 gauge or even finer) to help control the amount of solder applied.

Below are examples of good and bad joints:
Notice how you can see the outline of the pin in the middle OK joint, which is the best.
It can help if you get a scrap PC board and practice unsoldering and soldering the joints. Practice makes perfect.



To use solder wick, you may need to use a hotter iron, since the copper wick conducts away a lot of heat.
Fluxing the wick beforehand with rosin flux, as you mentioned, is a good idea.
 
Last edited:

jpanhalt

Joined Jan 18, 2008
9,050
My comment ( Post#2) about maximum temperature was based on personal experience and theory. I found some substantiation for that at Indium Corp.
https://www.indium.com/blog/hand-soldering-tip-temperatures.php
One of the biggest issues associated with high temperature hand soldering has more to do with the flux than the solder alloy. Most solder fluxes, regardless of form (liquid, tacky, or flux core) are designed to withstand temperatures up to 350°C. Above these temperatures, they begin to decompose and blacken.
Another problem with too high a temperature that I forgot to mention is that decomposition of the flux can lead to more difficult residues to remove:
https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdf
 

djsfantasi

Joined Apr 11, 2010
6,335
You’ll likely have some joints with too much solder. A piece of solder wick will remove the excess. Often, just that operation will result in a good joint. However, sometimes you’ll have to melt the solder joint again and add a small amount of additional solder. SMALL is the operative word.

In the two cases of insufficient wetting, remelting the joint will be sufficient, PROVIDED you apply the iron to both the pad and pin. In some cases, a little more solder will be necessary. Other times, you’ll need to wick away excess.

I’ve found that with practice, you develop a “feel” for using the iron. If I’ve placed it correctly, ensuring both pad and pin contact, a three count before applying solder is about right for my iron.
 

JohnInTX

Joined Jun 26, 2012
4,008
Here are some links to NASA documents. I still have my little NASA soldering book. It has grown..

Soldering Basics - Big, lots of pictures
www.sal.wisc.edu/docs/Soldering%20Basics.pdf

Attached:
Technical Standard For Soldered Electrical Connections
Student Workbook For Hand Soldering

Probably lots more by searching NASA soldering.

Good luck!
 

Attachments

Yaakov

Joined Jan 27, 2019
1,612
Question:
Can you solder too hot? Anyone have tips (no pun intended)? Is it me? Is it my iron?
Lots of good information here, but I;Llc add something i don’t think I saw.

Preactical soldering irons do not maintain the set point on the tip temperature when thy come in contact with the work. They lose heat to it (in heating it up) and so the temperature sags. The amount of loss is dependent on the thermal mass of the work vs. the thermal mass of the iron, and the ability of the iron to replace the lost heat with its own heater.

A good iron does this better. So, with a good iron you can choose a lower initial temperature (a good thing) and still make a good solder joint. You will have to leave the iron in contact with the delicate component for less time, heating it less, and being less likely to do damage.

Modern irons used direct heating. That is, the tips and heaters are integrated, unlike the older design where the tip slides over the heater. The latter has poor thermal transfer so there is a lot of loss and the tip heats more slowly.

There is a very inexpensive iron currently available for about $50 that uses the same tips as a Hakko 951, a venerable commercial grade iron, and has gotten universally good reviews. You can buy it, and buy genuine Hakko tips which are excellent, or third party tips which are cheaper and some are quite good.

You can find it here: https://m.banggood.com/Mini-V3-0-T12-Digital-Temperature-Controller-Soldering-Station-Soldering-Iron-Tips-T12-K-p-1338117.html

Please note, there are quite a few versions ot this station and this one in particular is specially good. The handle in particular, works like the Hakko while others require unscrewing a collar.

Good luck.
 

pmd34

Joined Feb 22, 2014
503
Hi Tentmaker,

Regarding your solder wick, it sounds like it could have oxidised a little. It usually helps to add a little extra flux to the joint when using the wick.
As one reply also commented you could be up against the horrific lead free solder which needs higher temperatures to melt. The easiest way to address this is to actually add some additional leaded solder to the joint with an iron first to dilute it!

Regarding iron temperature, the iron tip should melt solder placed on its tip easily. If its too hot you flux will tend to char, you might find PCB tracks delaminating from the board, and components with plastic parts will start to melt. You have to make sure your soldering iron can deliver enough power however. If the tip is too small, even if it is "hot enough" it cannot conduct enough heat into the solder joint to fully melt it. So for example you would not use an iron tip that you do small SMD work with, to solder a big diode.
It can also be a big trouble with trying to repair modern phone PCBs etc, that components are so well "thermally connected" that its extremely hard to desolder them with an iron, and you may have to resort to a hot air gun.

For re-soldering fine connections such as HDMI I would recommend a syringe + needle with some tin/lead/silver solder paste and maybe a little drop of additional flux. The silver really seems to help prevent getting an oxide skin on the solder while it is molten, and it flows wonderfully.
 

djsfantasi

Joined Apr 11, 2010
6,335
One final point I neglected to mention is that the tip needs to be clean. VERY clean.

After every joint, I wipe the tip on a damp cloth. After every few joints, I melt a little solder on the tip and wipe it clean. You can also use a metal scrubby to clean the tip. They’re available in the dish washing section of a supermarket. A copper scrubby is best.
 

Thread Starter

Tentmaker

Joined Feb 16, 2019
2
Thank you everyone for your input. What a truly wonderful community you make this forum!

Hats off to you all, as, with all of your expertise and experience, were bang-on regarding what likely was happening even before I had a chance to respond or see your messages!

Advice on:
--iron quality
--iron tip cleaning
--iron tip size
--wick's oxidation, its thermal conductivity, and its thermal mass
--dealing with lead-free/ROHS compliant solder
--diluting solder on boards with leaded solder
--using silver solder (avoided it but I want to try hoping it will make this a nice job)

...was great and truly appreciated!

Now, to add, at YouTube University, I did hear a pro talk about PS4 Motherboards in particular having large thermal mass as part of its cooling design, which makes sense now in hindsight, especially with my not-so-fancy soldering iron. All in all, everything lines up with a lot of what all of you have been saying. So, I might actually invest on the iron that Mr. Yaakov suggested as I do want to continue this interest of mine--thank you!

As for the science: It seems that the rate of thermal transfer from tip to pin in context of the thermal conductivity, thermal transfer, and thermal mass of the big PS4 board is part of the problems I faced which explains why I had more trouble than I did in the past. Also, the "horrific" lead-free solder (as it was humorously pointed out) was likely an issue and good point! Oxidized braid was also an issue that was pointed out here that I figured after noticing the copper being slightly blacked.

That said, if you don't mind, here is a follow up on the PS4 in intensive care:

I ended up buying some tin-lead solder paste, silver-solder paste, no-clean syringe flux, and a new wick (in realizing the braid was oxidizing over the year I had it) mostly made by MG chemical the next day I posted this thread. After being puzzled and disappointed after a few attempts to dislodge our HDMI port in desperation, My little buddy and I ended up getting the HDMI port off with a heat gun since the mounting pins would require heat simultaneously to lift off the connector. At first it was not working when we tried lower temperatures that were above melting point. Went for 18 minutes with no avail considering the boards thermal mass. We ended up cranking the heat gun to max (1350 F) with a make shift heat-gun station (cookie tins, foam tile, ceramic tile on carpet floor holding up board balanced by gravity), and to our excitement and a lot of cheering, we saw the solder liquefy and shine and we victoriously pulled it off with tweezers. We timed about 1 minutes 40 seconds for the solder to melt with a stopwatch apps on a smartphone. This was especially awesome because my little buddy, who usually wanted to gloss over the science-y details, actually said he had so much fun figuring this out with me and said it was really interesting to see how soldering worked while I used the iron. (And, tacos from taco bell were had as a reward!) So, thank you all for your friendly advice and support as it allowed us to not be discouraged.

As for the PS4 now: Trying to solder a new HDMI port down has been okay but not that great. We may have mangled the first HDMI port with a pair of jewelry pliers so I ended up repeating the surgery again to put another new HDMI. Practice makes perfect as you pointed out, and this time round it went more smoothly. But, I had an issue with solder bridges on the pins, using a tiny tip for the soldering iron. I think my little buddy bought an HDMI port with very short pins that protruding through some annoying plastic backing. Still, the plastic got in the way, melted in my carelessness, and got on the tip and made the solder ball up (like water on a hydrophobic surface). After not getting any wetting action, realizing what was happening, rubbing alcohol and tip cleaning saved the day. Desperate times called for desperate measures: I cut away the unnecessarily excess plastic with a scalpel (McGyver'ed it) to allow solder to wick up the pins better and stop bridging. I used paste (I don't like to use it because of the powdered lead). I used 22AWG solder (the smallest I could find at the electronics store). Not happy about the result and can't tell if there is bridging on the pins with my made-in-china magnifying glass with LEDs. Another desperate McGyver: Used a knife to cut between the pins just in case to make sure there are no bridges, but it feels awfully shoddy. So, I may use silver as pmd34 brought up here to do this right!

Thanks for all your help thus far :)
 
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