From my experience, Cardas melts at a higher temperature than Wonder and would be far from my first suggestion if one is re-flowing existing connections. The key word to that sentence is "flowing" and Cardas doesn't flow all that well. Wonder Solder is the easiest to work with out of all of the solders that i've tried in terms of application, melting point and quality of connection. It flows like no other solder that i've tried, making it easy for those that are less experienced to produce excellent results.
As mentioned above, the flux has to "attack" and "clean" the parts being connected in order for the solder and leg of the component to properly bond. It is the flux inside the Wonder Solder that makes it so good, which is why it flows and bonds so well. If the flux wasn't as good as it is, the solder would tend to clump up in one spot rather than flow. This would be due to the lack of a clean mating surface in the surrounding areas. Cardas tends to "clump" much more than Wonder even though some claim that it "sounds" better. While the Cardas may actually sound better, unless your skilled at soldering, i can't recommend anything any higher than i do the Wonder.
As for the Kester solders, Jon Risch is a big proponent of them, along with Belden products. Both are long time industry standards that are Chicago area based, but that doesn't mean that they are as good as it gets. I've got some major problems with Belden, but i'll save that for another thread : )
With that in mind, i've tried several different Kester's and they are all good solders. Having said that, they are all produce very heavy fuming, which is probably more hazardous to your health. Given that the Ersin eutectic solder that John Curl used to recommend is no longer being sold by Digikey, they are cross-referencing this part number to a eutectic silver solder that Kester makes. Once again, it is a good solder, but it produces a LOT of smoke.
I bring up the Kester solder as one can buy a pound of it for what you can buy an ounce of Wonder Solder.
The Kester part number is 24-7150-0026 and can be found here at Digi-Key if someone is interested.
From what i understand, Moncrieff basically duplicated the original solder formulation that Tektronix came up with for the manufacturing of their test equipment. This could be nothing more than a rumour, but i don't doubt it. Either way, the proof is in the pudding and whatever it is, Wonder surely is based on a good recipe. Like all of the other "specialty" solders though, it is VERY expensive.
While we are on the subject, here's a few tips for those that don't have a lot of experience soldering.
1) Keep your tip clean. That is, wipe your soldering pencil ( NOT a gun or "iron" ) on a DAMP ( NOT "soaking wet" ) sponge. After doing this, very lightly plate the tip with solder occasionally.
2) Use a small gauge solder. Most people have poor soldering equipment and skills. Using a heavier solder is one of the most common mistakes. First of all, it is harder to work with and to get into tight spots with. Secondly, the "junky" soldering irons can't keep up with the thermal losses encountered with heavier solders, causing the solder to clump up rather than to flow. By using a smaller gauge solder, you avoid those two problems. First of all, the solder is more easily maneuvered due to being skinnier. Secondly, the smaller amount of metal dissipates less heat, allowing the tip to stay hot enough to properly melt the solder. This allows the solder to flow better, forming a better joint. Thirdly, due to the smaller diameter and less clumping, one can more easily see the joint that they are working on and flow / apply more solder as needed. This works much better than just "glomping" solder onto the components "hoping" that it bonds.
3) Make sure that each of the pieces to be joined are clean. That is, you can't solder very well onto something that has a lot of corrosion and / or an enamel or paint coating on it. Scrape off all of the material till you get down to clean bare metal.
4) If soldering wires together or materials with long leads or legs, form a solid physical connection with the materials first and THEN plate that connection with solder.
If you are making a connection between a piece of wire and a component leg or the trace on a board, LIGHTLY plate each connection point individually and then bond them together with more solder as needed.
By plating each connection ( other than two wires or devices with long leads ), you reduce the necessary heating period when you're trying to bond them together. By placing them in close proximity to each other and then flowing more solder into the area, the fresh solder can bond to the existing solder plate on each surface. This is much faster with less potential damage than having to wait for the entire surface area to come up to the melting point, allowing the flux to clean the point of connections and then have the solder bond to each of surfaces individually. The solder that you are adding will flow onto the plating that you've already applied very quickly, making a good joint with less thermal stress.
5) Proper ventilation is required, but the rapid flow of air over solder joints is not good. As such, if you're going to use a fan to help dispurse the fumes, have it sucking air away from you and the solder joints, not blowing across it. Solder joints take some time to fully form, so don't "help them out" by trying to cool them faster via blowing on them.
6) Invest in a pair of
straight hemostat's,
curved hemostat's and
helping hands. You won't believe how much easier it is to solder with these tools and some good solder of the appropriate gauge. In case your wondering, a "good" gauge for solder is 26 or .031 diameter. DO NOT buy "generic" solder from Parts Express as it is very low grade. They are a good source for many different things, but NOT for low priced solder.
7) If you think that you have made a bad connection, it's not the end of the world. Try to remove / separate the pieces while applying heat for the shortest time possible. The use of
solder wick in such a situation can be quite helpful.
Once you've got the area cleaned up, take your time and do it right the next time. Getting frustrated means more potential for a bad joint, so relax and / or get up and take a break if it comes to that point.
8) Last but not least, invest in a "decent" soldering pencil. Most of the stuff at Rat Shack is crap, but it can work in a pinch. While casual solderers don't need a full blown Weller or Hako temperature controlled solder station, the purchase of a good 40 watt soldering pencil with the appropriate tips is an invaluable investment. You'll find that the more that you use these tools, the more that they will pay for themselves AND make your lives easier.
While i shouldn't have to say this, i'm going to anyhow. ALWAYS make sure that whatever you are working on is unplugged AND fully discharged. Some devices run at VERY high voltages and contain capacitors that can either knock you on your ass or even kill you. I'm NOT joking about this. If in doubt, turn the item off, unplug it from the wall and then turn it back on. After letting it sit with it turned on but unplugged for at least 30 - 60 minutes, you should be okay. This is a very vague generalization, so PLEASE be safe rather than sorry. If in doubt, give it 24 hours and then come back to it. Having an inexperienced "DIYer" shoving his hands and 120 volt soldering pencil into an expensive and potentially lethal electronic device can be scary enough as it is without making very costly and / or deadly mistakes.
Hope this helps and that you remember "Safety counts". After all, it is your gear, your money and your health that you're dealing with. Sean
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