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

On 7/3/2017 11:57 AM, 'Technotronic~Dimensions' 
infotech@... [Homebrew_PCBs] wrote:
>
> 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:
>
>