Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Steve,

With regard to dissolving epoxy, I have good news, and I have bad news. The good news is that there are chemicals used for depotting encapsulated assemblies.

Back in the days before dirt was invented, I ran a failure analysis lab for my employer where my technicians used several chemicals from Dynaloy. They were sold under the Dynasolve product line. We also used another product of theirs called Decap. Here is a website for one of their distributors: http://www.ellsworthadhesives.ca/manufacturer/dynaloy

I note that they now have a greater variety of chemicals than were available "way back then."

That being said, there are a few issues (the bad news):

1. The chemicals don't dissolve the epoxy. They swell the epoxy and cause it to flake off. Active removal (scraping) is required

2. I think we had to match the chemical to the epoxy cure system, i.e. amine, phenol, etc., to get the best performance. I don't know if this is more or less so now, with the greater number of chemicals available  today.

3. Since the circuit boards are usually epoxy impregnated, they will suffer as a result of this treatment. Any other parts that are epoxy encapsulated, or made with certain plastics would likely be adversely affected.

4. To say that the chemicals were pricey, would be a gross understatement. We bought them by the gallon, and each gallon cost an arm, a leg, and someone's first born son.

The chemicals did the job for us because our usual need was to retrieve the failed components from the assembly. We had little concern for the assembly itself. The items we were after were in metal or ceramic packages, and therefore were not affected by the chemicals. Although the possibility of removing the epoxy and repairing an assembly exists, it is expensive and labor intensive, with a low probability of success.

On the very rare occasion that a module had to be repaired because there was no other choice, a different technique was used. This technique is not generally available outside a lab like ours, but I present it just in case you have access to the necessary machinery/information.

This technique requires good information on the construction of the module. We started by performing X-Ray in X, Y and Z axes. The X-Ray results were compared to the original assembly drawings, and the component of interest was located. By using extremely precise drilling and milling tools, combined with progressive X-Rays, a cavity was made around the part to be replaced. Every attempt was made to make the cavity very close to the part. The cavity was then filled with the chemical of choice, and the epoxy slowly scraped away, exposing the component. Just watching this process was painful. I don't even want to discuss how difficult it was to replace a component once the cavity was open and the defective component removed.  To underscore: this was only done when there was no possibility of getting a replacement module, or the time it would take to get a replacement would have a devastating impact on delivery schedule.

Harvey A

 

Hi

Sorta new here and trying to catch on to some of the procedures described
here.

Was wondering if anyone knows if theres a chemical or chemicals (s) that
will safely dissolve epoxy that some manufacturers
use to encapsulate boards to protect them and make them more or less
unservicable when a component fails?

I have hears there is a chemical that they can be soaked in for many days,
and you have to check on it daily before it eats through
things that u dont want it to damage.

Steve Hearns
Technotronic Dimensions [USA]
WWW.TECHNOTRONIC-DIMENSIONS.COM
1.518.663.3421 (MAIN)
1-877-817-9885 (Voice / Fax Toll Free - US Only)
E-Mail: Steve@...
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----- Original Message -----
From: "LEON HELLER leon355@... [Homebrew_PCBs]"
<Homebrew_PCBs@yahoogroups.com>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, July 03, 2017 12:56 AM
Subject: Re: [Homebrew_PCBs] Ferric chloride staining PCB substrate

Oxalic acid removes ferric chloride stains. I've got a big bottle of it
somewhere but have never used it.
Leon

On Monday, 3 July 2017, 2:56, "'Brad' unclefalter@...
[Homebrew_PCBs]" <Homebrew_PCBs@yahoogroups.com> wrote: