A "Good" Soldered Connection

[David Meek]

Hey Poobahs ;x( I've got a couple of questions on soldering for you.

What makes a good soldered connection? And what benefits will someone get from one of these over one that simply works?

I've got the woodworking end of things covered pretty handily, but on the internal component construction side of things, I'm just a rank amateur so thanks for your knowledge.

[JonMarsh]

In my day job, power semiconductors, a good soldered connection is a pretty big deal, because with surface mount transistors smaller than a postage stamp and and on-state resistance of 2 milli-ohms, handling up to 50A, that small solder connection is critical to performance and long term reliability. And there's a lot of expensive qualification and reliability testing that goes on to verify that before a product is released.


I'm going to cut to the chase, though, as far as my recommendations, especially for handwired connections and building speakers, as the requirements are somewhat different than for high performance power conversion in surface mount!

Two essentials for "good" solder connections, in my opinion.

One is technique; using a good temperature controlled iron, using it properly to heat the items to be soldered FIRST, then flowing the solder onto the heated wires.

Second is choice of solder alloy and flux. A eutectic alloy is one which melts and solidifies at the same temperature. In practice, this doesn't always happen uniformly with standard 60/40 lead-tin solder; witness, the phenomena of non-shiny "cold solder" joints, which can occur when one metal slurries out or solidifies before the other, especially if disturbed while cooling. My personal preference is for Cardas Quad Eutectic solder, which is a eutectic alloy of lead, tin, copper, and silver. It has very good material properties regarding conductivity, and is the most "bullet proof" I've found to creating consistently good solder joints- more than any other solder I've seen, it's slurry resistant and seems to cool to a nice shiny hard finish. :T There's no point spending $100 on a tweeter, and mucho bucks on crossover components, then skimping on the solder.

Just my 0.02. :B



~Jon

[David Meek]

using a good temperature controlled iron, using it properly to heat the items to be soldered FIRST, then flowing the solder onto the heated wires.

With that, my current iron is not up to par. Would this unit be a good choice in quality, performance and cost? Weller WTCPT. Or, what do you recommend?

My personal preference is for Cardas Quad Eutectic solder, which is a eutectic alloy of lead, tin, copper, and silver. It has very good material properties regarding conductivity, and is the most "bullet proof" I've found to creating consistently good solder joints- more than any other solder I've seen, it's slurry resistant and seems to cool to a nice shiny hard finish. :

Okeedokee, the best price I've found on it is $38.00 for a 1 lb. spool. Does that sound about right? Also, on conductivity - with all other things like component pieces, tools, materials being equal, how does a poor-quality join affect things in a speaker? I guess what I'm asking is if something so simple can affect a speaker's sonic qualities?

[Dennis H]

One is technique; using a good temperature controlled iron, using it properly to heat the items to be soldered FIRST, then flowing the solder onto the heated wires.

Just to expand a bit on what Jon said, assuming we're talking about crossovers....

First make a good mechanical connection by twisting the wires together. The solder is just there to make the electrical connection.

Wipe off the tip of the hot iron with a rag, sponge or whatever and dab a little solder on it so the tip is shiny.

Heat the wires until they are hot enough to melt the solder. Dab the solder onto the wires, not the iron's tip, and it will start to flow when the wires are hot enough.

After you flow on enough solder, remove the iron immediately so you don't toast the components. Try not to jiggle the wires until the solder hardens. If you get a joint where the solder looks rough and sludgy rather than smooth and shiny, remelt it and let it cool again.

[ThomasW]

Jon and I have used the Weller WTCPT solder stations literally for decades. They are our irons of choice ............... :T

The Cardas is the Rolls Royce of solder. There are several brands of 2% silver solder that sell for ~$18/lb. That's what I use.

Most of the time a solder joint has to be an open circuit for current not to flow. 'Cold' solder joints (dull looking) usually make a circuit but it's not an optimal one. A proper solder joint looks like chrome plating, very bright and shiney

[JonMarsh]

Dennis H's description is very good. Sometimes for prototyping I just tack solder, but having a good mechanical connection for finished work is very desirable.

As Thomas notes, we've been using the temp control workstations for ages. But you don't have to spend $150+ to get decent results- Weller has some entry level units worth considering.

Weller WPCL100

Once again, PE comes through.

I also noticed yesterday in the flyer that came with my parts order that they have Behringer Feedback destroyers now.

David, I tend to pick what tools and materials to use based on the idea that I want to minimize the cumulative effects of each connection and interconnect. The solder you found for $38 a lb. is the stuff I use. George Cardas is not "technical" in the sense that a physicist is technical, but he has an acute ear (does a lot of recording work, too), and a very wide range of materials knowledge- this has been applied rigorously over decades in the development of his products, and often in cooperation with his major OEM customers, including companies like Ayre Acoustics. So, ultimately, it's up to you to decide if you want $6 a spool solder, or $18 a spool solder, or $38 a spool solder. There are a lot of solder connections in one of my crossovers, so I want to make sure each one is first class.

From Welborne labs, and probably other sources, you can buy a smaller quantity, and try working with it. Because of both the ease of working (very consistent cooling and hardening- doesn't have some metal slurry out at a different temp than another), and the mechanical and electrical characteristics this stuff has become the only solder I use. This stuff is used in CARDAS cables, of course, and that was one of the main development reasons.

But I recognize that though I bottom feed when possible, about things I care about I'm a bit of a fanatic. This is one of those things... When the very best costs only a little bit more, why settle for less?

~Jon

[David Meek]

This stuff is used in CARDAS cables, of course, and that was one of the main development reasons.

I noticed that this Lex guy uses it in some kind of cables he makes, too. :W

[Al Garay]

David,

Like anything else, shop around. I have seen the WELLER WTCPT for as low as $75 for a new station. Google is your friend.

The Cardas solder is perfect for a relative beginner (like me) who needs confidence. It makes me feel competent. But, work in a well ventilated area and wear a mask.

Al

[David Meek]

All right, you guys are helping the "bug" to catch hold here. :B

Weller makes both of these, so here's another question. Would it be better to go with the WTCPT model which varies temperature by changing tips on the wand, or would a dial-adjustable model like the WES51 be preferable?

So far, the best I've found is either one new for $109 at Crawford Tool.

[JonMarsh]

I have both; for most work, the number 7 tips are the ones to have. I use this one for crossovers.

But I like the variable output model 51 for fine work on PCBs.

That seems to be a good price.

~Jon

[Ten 99]

Great Topic. Lots for me to learn. Making notes for sure. Most of this information is all new to me. I have a crappy 40W Ratshack iron and some silver solder. I have never known what is a good iron, and what to look for.

I have seen a brand at Fry's called Haiko. Are these any good? If Weller is the brand to stick to, then I'll definitely just take the recommendations above. I also don't mind paying the $38 for solder, knowing that it works better and will likely help a novice like me have an easier time at making good joints.

Thanks for the quality questions and answers.

I have also been reading a lot about DIY amplifiers and DACs, and having a good soldering setup would be good if I can work up the courage to try some of these things out. By comparison, the Xovers shouldn't be very difficult at all. But now we're being given formulas for balanced power, etc. Wow, what a great feeling.

[ThomasW]

http://www.itcelectronics.com/pdtl-revised.asp?P=3331

[Al Garay]

Hakko and Weller are both considered excellent brands that will do very well. It's like comparing SnapOn and Mac.

In general, I have found better deals on Weller. The tips are readily available and fairly inexpensive, around $5 whereas the Hakko costs more like $15. I bought the Weller station just because it was a great deal. It's plenty good enough.

This site had the Weller WTCPT for $79.99. You might ask to see if the price is still available.

Al

[David Meek]

I have both; for most work, the number 7 tips are the ones to have. I use this one for crossovers.

But I like the variable output model 51 for fine work on PCBs.

You just answered THAT question Jon. It's the WTCPT for me as I don't plan on working on PCBs in the foreseeable future. Speakers wiring, X-overs and maybe a big balanced power unit (if I get that ballsy)!

I have a crappy 40W Ratshack iron and some silver solder. I have never known what is a good iron, and what to look for.

That's me, hence the questions. :

I also don't mind paying the $38 for solder, knowing that it works better and will likely help a novice like me have an easier time at making good joints.

Ditto.

Thanks for the quality questions and answers.

Yeah, it's so cool having guys like Jon, Thomas, Al and Dennis around. Oh yeah, and Hank and . . . . What a group! :T

[awm]

Just to add to the mix, here -- I completely agree that quality solder is very important. My preference is for the 4% WBT silver solder, available from PE. It has one of the lowest melting points I've seen and hardens to that chrome-like finish every time -- and silver is actually pretty strong. I also like that it doesn't have lead, so I have no lead fumes wafting around my house... Downside? Cost, like all WBT products... (I've used the Ratshack 4% silver stuff and there is no comparison. The Ratshack stuff constantly produced the dull joints that have been mentioned.)

My understanding of soldering is not that it creates electrical connection but that it maintains one already established by good mechanical connection, that might otherwise be lost through movement, shaking, etc. Essentially, it fixes an established connection. In the ideal, theoretical world, you want the circuit to be able to function WITHOUT solder through good, mechanical connection. The reason I belabor this is because I think it's a useful mindset to adopt. And, having done so myself, I've (knock on wood) never had a cold-solder joint...

Finally, get a dial temperature control Weller. The WES51 is perfect because it allows the most flexibility. This plus good solder will be a huge step up if you've been using Ratshack stuff... You'll feel like a master!

Andy

[Hank]

AWM, you are correct. Solder ensures a zero resistance electrical connection, but should not be relied on for mechanical strength. Make a strong mechanical connection, then solder it and you're in "connection heaven".
No groans, please. :roll: