Electrolytic : How to tell a good bar from a bad one
Most people buy bar solder like they buy gasoline – the cheapest price is what they go with. That is a costly mistake. There are different grades of solder and these differences can save a company a lot of money. The problem is how to tell a good bar from a ‘not so good’ bar. They look the same, and the salesman will tell you the bar you are buying it the best. Well it is actually pretty easy, but you need to get the right information and understand it. The first step is to ask for the analysis.
Sn63/Pb37 Bar Solder in the web store
SAC305 Bar Solder in the web store
Element |
Name |
Typical MRI Bar Solder |
Typical Solder Sample |
Likely Source of the contaminate |
Cu |
Copper |
0.005 |
0.085 |
Board metallization or component barrier layer |
Au |
Gold |
0.003 |
0.027 |
Board or component flashing |
Ni |
Nickel |
0.005 |
0.0044 |
Component barrier layer |
Ag |
Silver |
0.001 |
0.031 |
Component termination |
Sb |
Antimony |
0.001 |
0.073 |
Likely introduced in the raw bar |
Bi |
Bismuth |
0.001 |
0.026 |
Likely introduced in the raw bar |
Cd |
Cadmium |
0.005 |
0.0011 |
Likely introduced in the raw bar |
In |
Indium |
0.001 |
0.0048 |
Likely introduced in the raw bar |
Fe |
Iron |
0.005 |
0.0034 |
Likely introduced in the raw bar |
The analysis shows the trace elements in the bar that are not what you are buying. As the solder is used, the molten metal leaches off metallization from the boards and components going through the wave. These end up in the solder pot and cause problems. The process goes on until the contamination gets so bad; it falls outside the J-standard. The J-standard allows a really high amount of trace elements. It was written by bar manufacturers in a way that should allow pretty much anything they make to pass, and it does. What bar solder is made, reclaimed solder (full of contaminates) is assayed and virgin solder is added to drive the contamination levels down below the standards. Basically some makers blend off the reclaim with higher purity metal until they can sell you the reclaim back. This is great for prices, but it leaves the electronic assembler with a small window to work in before needing to add new solder. The trace contaminates lower the ability of the solder to flow and cause more defects. The rate of oxidation is also higher, so the dross production is higher.
So the first step in figuring out if you are buying good stuff is to ask if it is reclaimed, virgin or electrolytic. Also ask for an assay showing the contamination levels. They ALL will pass the specifications, but this not what you want – you want to get the lower levels of contaminates.
What is Electrolytic Solder?
So you know it is best to get the lowest level of contamination. And the chart shows electrolytic solder is the best, but what is it? The Electrolytic process is like a plating process. The metal is places in an ionic bath with a current allied over 2 plates. One plate has a metal plate with contaminates, the target plate attracts atoms of elements. That is pure metal (Tin, Lead, Silver, and Copper). Different baths and different currents catch different elements. The contaminates drop to the bottom of the tank and all that remains is a target plate of a very high purity.
When the contaminates are not in the bar you buy, several good things happen: This purity results in a lower viscosity and surface tension. This results in a lot less bridging, icicling, and cob-webs. The ability to flow over the board is better (Lower viscosity and better surface tension) and this means the wave solder machine can run more efficiently and in some cases – faster. The batch to batch consistency is much much better and this also makes the process engineer’s life easier The yields go us, the dross goes down and the costs are much lower. Electrolytic Solder may be slightly higher is cost, but this is very slight. The benefits are large. It is much more cost effective.
Sn63/Pb37 Bar Solder in the web store
SAC305 Bar Solder in the web store