It seems that nothing else is more polarizing and generates more passionate debate then our recommendation to customers to use acid based flux for soldering trackwork. The topic comes up regularly both in this and other modeling forums with experts lined up on both sides of the acid vs. no (low) acid flux issue.
On one side we have many people saying that you should never use acid based flux. Period
And then you have the other side (namely us, Fast Tracks) recommending that you should always use acid based flux for soldering trackwork.
So what is the story here? Why do we recommend acid based flux, and others recommend against it? The fact is, both answers are right. Both flux types will work just fine. But there are important reasons why we recommend acid based flux over low acid flux for soldering trackwork.
To try to explain why we advocate the use of acid flux and answer the questions that keep coming up about this, we have produced the following list of Frequently Asked Questions (FAQ).Why do you recommend acid based flux?
Acid based flux will always give you better results with less effort and is highly recommended for folks who are new to soldering. Even if you are an experienced solderer, we still recommend you use acid based flux as you will always get consistent, high quality results.Why do others recommend low-acid based flux?
It is felt by some people that using an acid based flux will result in corrosion problems over time. However we have found that as long as the finished trackwork is properly cleaned, this is not an issue. We have trackwork that is over 15 years old that was soldered with acid based flux and not cleaned
that is still as solid as the day it was made. (Although we do of course very much recommend that you always clean your trackwork after soldering.)I was always told to never use acid flux for wiring and electronics. Why is it OK for soldering trackwork?
This advice is correct, acid based flux should never
be used for soldering wire joints or electronic components. Soldering trackwork on the other hand is more akin to soldering plumbing joints than electrical joints. You are more interested in producing mechanically sound joints than electrically conductive ones. And like plumbing, acid based flux is recommended for producing robust, mechanically strong joints.Won't the acid corrode the trackwork over time?
As long as the finished trackwork is properly cleaned, the trackwork will not corrode over time.How should I clean trackwork soldered with acid based flux?
We recommend that the finished trackwork be cleaned with a wire brush. You will find complete illustrated instructions on pages 42 & 43 of our soldering document that is included with every order that we ship, or on our website here:http://www.handlaidtrack.com/documents/ug01.pdfShould I use baking soda to neutralize the acid?
You can, but it is not really necessary. If you are concerned about corrosion over time it is an extra step that you can take that will completely neutralize any remaining acid after brushing the trackwork with a wire brush.My solder joints look fine and I just use low acid flux. Why do you still recommend acid based flux?
We have seen hundreds of examples of finished trackwork from our customers, and while many people believe they are getting good results with low-acid flux, we have found that many examples are not as good as they could or should be. A sound joint will have solder that has completely liquefied and flowed between the rail and PC Board tie. Getting the solder to a fully liquefied state is usually not a problem, but getting it to 'flow' in between the rail and ties takes a bit more practice. Acid based flux makes it considerably easier to get the solder to flow, resulting in a solder joint that is very smooth and flat.
Here is a good example of sound solder joints.
If you study this image carefully you will notice that the solder just 'wets' the tops of the ties, gently rising up and over the bottom of the rail. The joints are smooth and void free. These types of joints are very possible with low acid solder flux, but are much harder to produce. Acid based flux on the other hand makes it much easier - and is quite safe over the long term.So which is better? Acid or no-acid flux?
Both will work fine. If you are new to soldering, we recommend acid based flux. If you are an experienced solder, then using low-acid flux will do the job, although you will always get better and more consistent results with acid based flux.
Our objective is to provide the best tools and advice to our customers so that they are able to produce robust trackwork that works reliably over time. And sound, well formed solder joints are a key part of that objective. Acid based flux increases your probability of success, which is fundamentally why we recommend it's use. Corrosion issues over time on the other hand can easily be mitigated with simple cleaning techniques.