joint brightness and percent of core flux

Thread Starter

PeteHL

Joined Dec 17, 2014
268
Today I finished a spool of Sn60/ Pb40 solder with 3.3% flux, 0.8 mm diameter. Now I'm using solder that is Sn63/ Pb37 with 1.1% flux, 1mm diameter. Comparing the brightness of the previous solder joints to what I am making now with the new spool, the previous joints are much more shiny. In fact by comparison the joints prepared with the new spool are quite dull. I'm heating the joints the same as before. Should I be concerned about the new joints being less shiny, or is this just because of the lower percentage of flux?

Putting together a circuit that I don't want to spoil after a lot of developing it,
Pete
 

djsfantasi

Joined Apr 11, 2010
5,907
Since the solder ratio is different, the amount of required heat will change. If you’re hearing the joints the same as before, I’d say you weren’t hearing them enough for the new solder.
 

BobaMosfet

Joined Jul 1, 2009
927
Today I finished a spool of Sn60/ Pb40 solder with 3.3% flux, 0.8 mm diameter. Now I'm using solder that is Sn63/ Pb37 with 1.1% flux, 1mm diameter. Comparing the brightness of the previous solder joints to what I am making now with the new spool, the previous joints are much more shiny. In fact by comparison the joints prepared with the new spool are quite dull. I'm heating the joints the same as before. Should I be concerned about the new joints being less shiny, or is this just because of the lower percentage of flux?

Putting together a circuit that I don't want to spoil after a lot of developing it,
Pete
Get yourself a bottle of flux. You can put a dab on the join and reheat, and that may help. You may also find (but check this carefully) that you can use a toothbrush with iso-propyl alchol to clean dried flux off the board perfectly for any PCB work you do.
 

DickCappels

Joined Aug 21, 2008
6,068
I echo BobaMosfet's remarks. I keep neutral PH flux paste next to the soldering iron use it liberally. The joints are usually beautiful.
 

kubeek

Joined Sep 20, 2005
5,654
Different alloys have different appearance after they solidify, but in my experience 63/37 usually is shinier than 60/40.
 

dl324

Joined Mar 30, 2015
9,543
My experience is that joints made with 63/37 are brighter than 60/40, but it's been a long time since I used 60/40. 63/37 has fewer problems with cold joints (which are dull) than 60/40 because 63/37 is eutectic.
 

Tonyr1084

Joined Sep 24, 2015
4,017
The level of shininess should not be your main concern. If the solder shows evidence of good wetting to the lead and the pad then it's a good solder joint. For years I worked in the industry and had to argue with people who insisted the solder joint had to be shiny and shaped like a Hershey's Chocolate Kiss. According to IPC-A-610 rev G, that's not true. A class 3 solder joint can be up to a minimum of 75% filled through the through hole. Surface mount devices need to have a fillet and good wetting. Extra solder does nothing for the joint. And with the expansion of RoHS solder (Removal of Hazardous Substances - a.k.a "Lead Free" solder), joints almost never look shiny. In fact, they can fool you into thinking a joint is disturbed or cold. But as long as there's evidence of wetting and the joint (class 3) is 75% or more filled or wetted - it's good. Class 3 is military, hospital, automotive, aerospace grade solder. Class 2 is more liberal and is more for commercial equipment like TV's, radios, computers and such. Class 1 is for children's toys. And looking at solder joints that meet only class 1 - they look like garbage.
 
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Thread Starter

PeteHL

Joined Dec 17, 2014
268
The level of shininess should not be your main concern. If the solder shows evidence of good wetting to the lead and the pad then it's a good solder joint. For years I worked in the industry and had to argue with people who insisted the solder joint had to be shiny and shaped like a Hershey's Chocolate Kiss. According to IPC-A-610 rev G, that's not true. A class 3 solder joint can be up to a minimum of 75% filled through the through hole. Surface mount devices need to have a fillet and good wetting. Extra solder does nothing for the joint. And with the expansion of RoHS solder (Removal of Hazardous Substances - a.k.a "Lead Free" solder), joints almost never look shiny. In fact, they can fool you into thinking a joint is disturbed or cold. But as long as there's evidence of wetting and the joint (class 3) is 75% or more filled or wetted - it's good. Class 3 is military, hospital, automotive, aerospace grade solder. Class 2 is more liberal and is more for commercial equipment like TV's, radios, computers and such. Class 1 is for children's toys. And looking at solder joints that meet only class 1 - they look like garbage.
Thanks, my only concern is that I'm getting a good solder joint. There is the rule of thumb that the joint should be shiny, otherwise it means that the joint was disturbed as the solder cooled or the joint wasn't heated sufficiently. Then a joint with a dull appearance means that it's faulty. There is not a problem with my iron delivering sufficient heat and I'm not disturbing the joint while the solder cools.

When you say wetting to the lead and the pad, do you mean that the solder flows to them and attaches?

Sometimes items from the supplier that I got the new spool of solder from are garbage. As Kubeek and dl324 have experienced, I would expect that Sn63/ Pb37 to be at least as shiny as Sn60/ Pb40 when the joint has cooled.

Applying flux to a joint before soldering shouldn't be necessary, I think.

Regards,
Pete
 

TeeKay6

Joined Apr 20, 2019
551
Thanks, my only concern is that I'm getting a good solder joint. There is the rule of thumb that the joint should be shiny, otherwise it means that the joint was disturbed as the solder cooled or the joint wasn't heated sufficiently. Then a joint with a dull appearance means that it's faulty. There is not a problem with my iron delivering sufficient heat and I'm not disturbing the joint while the solder cools.

When you say wetting to the lead and the pad, do you mean that the solder flows to them and attaches?

Sometimes items from the supplier that I got the new spool of solder from are garbage. As Kubeek and dl324 have experienced, I would expect that Sn63/ Pb37 to be at least as shiny as Sn60/ Pb40 when the joint has cooled.

Applying flux to a joint before soldering shouldn't be necessary, I think.

Regards,
Pete
Whether additional flux is needed depends on how "clean" the items to be soldered are. Both PCBs with nickel and solder coating and components with solder-dipped leads oxidize over time, becoming more difficult to solder. Of course other contaminants can be present as well. There are different fluxes available even with cored solder. You did not state what flux your solder contained. Why not experiment a bit with lower and higher iron tip temperatures to see what works best?
 

sagor

Joined Mar 10, 2019
131
63/37 solder has a lower melting point than 60/40, and should be a better joint.
63/37 fully melts at 183C, whereas 60/40 starts to melt at 183C but remains slushy until it reaches 191C.
https://fctsolder.com/eutectic-solder/

If anything, the amount of flux or the type of flux may be what is making the difference in the "shine" of the solder joint. Hopefully you have rosin flux in both of those, not acid flux (bad for electronics)
 

#12

Joined Nov 30, 2010
18,167
Here's another two cents worth. 63/37 is the mixture at which all the solder contents solidify at the same temperature. There is less of the slushy stage while cooling. You might say it grabs or solidifies suddenly. The lag time on 60/40 is what fools you into thinking the solder is solid when it's not. You let go of the wire and the solder joint moves while it's in the slushy stage and you have to do it over.

I have liquid flux because my solder wick oxidizes a little before I use up a roll. I can scrape it with my pocket knife and it works pretty well or I can dip it in liquid flux and it works like brand new.

Wetting is the act of the solder dissolving a little bit of copper. This forms a second alloy of metals at the solder to copper interface, lead+tin+copper. This should become obvious when you realize that all copper soldering tips slowly dissolve. That's why you buy, "ironclad" tips.

Maybe that was three cents worth...
 

MisterBill2

Joined Jan 23, 2018
4,817
Certainly the quality of the solder joint is what matters, except in some art sculptures. And the quality acceptable for consumer goods is not adequate for industry, where reliability is the main concern. So use some flux remover and examine the joint with good light and a magnifier, and if the wetting on both materials is adequate and the volume of solder is correct, then the joint is OK.
 

Tonyr1084

Joined Sep 24, 2015
4,017
When you say wetting to the lead and the pad, do you mean that the solder flows to them and attaches?

Sometimes items from the supplier that I got the new spool of solder from are garbage. As Kubeek and dl324 have experienced, I would expect that Sn63/ Pb37 to be at least as shiny as Sn60/ Pb40 when the joint has cooled.

Applying flux to a joint before soldering shouldn't be necessary, I think.
Wetting means the solder has molecularly bonded to the lead being soldered. It should feather into the lead and not look like a drop of water on a freshly waxed car (if you've ever waxed cars - a thing quickly becoming a distant memory).

The quality of the solder is another issue. Assuming you have good solder, when soldering, solder will exist in three conditions; solid, plastic and liquid. Solid - of course- is when it's cold. Liquid - self explanatory I think. Plastic is the period of time when it is changing from liquid back to plastic. You can also have a plastic state when heating solder, but usually it's not a concern because you're still heating it. Once it flows it's no longer plastic. As others have already said, 60/40 has a longer plastic period than 63/37.

As to flux, many things can affect how well a joint solders. One thing nobody has mentioned that I believe I've noticed is that touching the leads can leave oils on the parts. That, too, can be a problem. Cleanliness has already been mentioned. Additional flux is another suggestion already given. Therein lies another issue - what kind of flux. I'm not the flux expert but I can point a few different types. There's an aggressive flux that can make soldering look absolutely perfect, but it MUST be washed off. Some fluxes are water soluble, meaning it can be washed off with water. Others require a cleaning agent. There's also "No Clean" fluxes, meaning you can solder with them and then not worry about cleaning them off. Another factor in flux is the age. Solder can sit a long long time on the shelf. It can "Expire". Usually an unscrupulous manufacturer will sell those older solders off to a second seller, who will then sell them to a consumer (you or me) and not tell us anything about any expiration dates that have gone by. So there's lots of issues to contend with.

When soldering, after solder has flowed (wetted) both surfaces, if the joint moves you can get the appearance of a cold or disturbed joint. A cold joint is one that has never come up to temperature. It will exhibit poor wetting. As to learning what they look like, you can google IPC 610 and look at some pictures. I own a copy of the latest standard but have signed a document stating I will not disseminate any of the pictures or descriptions contained there-in. Still, you should be able to find some pictures on line. Maybe a YouTube video would help. Soldering is not difficult, but soldering well takes practice. The very first solder joints I made looked like they were made by a 7 year old using a Weller soldering gun and using solid core 60/40 solder. In fact, I WAS 7 years old. Blobs of solder on wires and switches, but they worked.

Wetting is the act of the solder dissolving a little bit of copper. This forms a second alloy of metals at the solder to copper interface, lead+tin+copper. This should become obvious when you realize that all copper soldering tips slowly dissolve. That's why you buy, "ironclad" tips.
Wetting action is an atomic bonding of alloys. And yes, they form a new alloy. And I second the comment about iron clad tips. I have a copper tip that was once a nice point but is now a hollowed out 7/16 inch dish. I rarely use the iron. Mostly for desoldering large parts because the tip brings so much thermal mass to the joint and really gets the heat penetrating the joint.

As far as the mention of lead free solder, those are much more difficult to work with. Oh yes, you CAN work with them and you CAN make a good looking solder joint. But it's not for beginners, that's for sure. As for expired solder, many of them can still be used. They work even better with the addition of a little flux. I personally have a bottle of #312 - Alcohol-Based No-Clean flux. It's a pen with a marker type of applicator. You press in on the tip and a little flux will spill out. The tip is used to spread it and coat the parts to be joined. Actually got it from Amazon. I know, Amazing. But yes, we sometimes buy from chancy sites. But we have to be willing to live with what we get. And not always will you get the best products.
 

Thread Starter

PeteHL

Joined Dec 17, 2014
268
Trying soldering a joint where I put some rosin flux paste on the joint first resulted in only a slight improvement of shininess. My hunch is that the new spool is defective solder with more lead than tin than what it is supposed to be. In other words, the actual mix is something like Sn 50/ Pb 50.
 

Tonyr1084

Joined Sep 24, 2015
4,017
No harm in running down to the nearest RadioShack and picking up one of those cheap tiny tubes of solder and giving that a test. Assuming you're in America, or RadioShack is international. Try a different solder and see what happens.
 

MisterBill2

Joined Jan 23, 2018
4,817
I have used old solder and cheap solder and various alloys of solder and certainly some work much easier to produce a good joint than others do. the condition of the surface of the things to be soldered is the most important variable, but not the only critical variable. A flux that gets past that oxide coating will allow a good joint, but not assure that it will be good. There needs to be enough heat so that the solder can make an adequate molecular bond to both surfaces, and enough solder to provide the adequate mechanical strength of the connection. Describing those variables was the subject of a paper that I wrote a couple of years back. If I can locate that file I will submit it to those who handle publishing on this site, it may be useful to a few folks.
Soldering is a bit like playing music well, in that not only is it important to know what to do, it is also a skill that takes practice.
 

Thread Starter

PeteHL

Joined Dec 17, 2014
268
No harm in running down to the nearest RadioShack and picking up one of those cheap tiny tubes of solder and giving that a test. Assuming you're in America, or RadioShack is international. Try a different solder and see what happens.
The joints of the circuit board that I made yesterday are partly with the spool of solder that ran out and the new spool. So it's not me nor the condition of the PCB and leads; the solder is the difference.

Here in coastal Maine Radio Shack and a small independent electronics store went out of business many years ago. As far as I know, there is no store in my area where I could find solder let alone at a reasonable price. Most likely it is true that in many other parts of the US it is not possible anymore to find a brick and mortar electronics store.

If there is less tin than there should be, how would this affect the solder joint?

Thanks for your comments,
Pete
 

TeeKay6

Joined Apr 20, 2019
551
The joints of the circuit board that I made yesterday are partly with the spool of solder that ran out and the new spool. So it's not me nor the condition of the PCB and leads; the solder is the difference.

Here in coastal Maine Radio Shack and a small independent electronics store went out of business many years ago. As far as I know, there is no store in my area where I could find solder let alone at a reasonable price. Most likely it is true that in many other parts of the US it is not possible anymore to find a brick and mortar electronics store.

If there is less tin than there should be, how would this affect the solder joint?

Thanks for your comments,
Pete
Try HomeDepot, Lowe's, or other hardware stores for solder. Even my local WalMart stocks some. Of course, an online electronics distributor has a much wider selection.
 

MisterBill2

Joined Jan 23, 2018
4,817
Try HomeDepot, Lowe's, or other hardware stores for solder. Even my local WalMart stocks some. Of course, an online electronics distributor has a much wider selection.
While the luster of the joints may differ a lot, the quality of the joint is determined by the way that the solder has bonded to the materials and how well it has bridged the gap between them. I would need a good magnifier and good light to see that difference, most folks can see it with just good light and a close look. If the solder has bonded to both surfaces then it is usually a good joint.
 
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