Graham

I used shellac/ethanol in the 1940s for the anode voltage (~1.8 kV) 
assembly for an oscilloscope I built using a 3BP1 war surplus CRT. No, I 
didn't clean first, but remember this was tag-to-tag wiring, not PCB.

Between then and acrylics, I used a phenol-formaldehyde formulation.

Brian

On 16/02/2013 00:04, Graham Naisbitt wrote:
> Hello everybody - IR Here!
>
> Question1 - Adhesion
>
> IMHO the problem is often derived from the presence of surfactants that have not been correctly controlled in earlier processes. "Correctly controlled" I acknowledge is an ambiguous term, but you need to go back to each process step and ensure that the process has been properly carried out: Solder resist - soldering processes - masking processes etc..
>
> That said, the fact is that certain acrylic based coatings exhibit poor adhesion and one solution to this is to bake the assembly at around 80DegC for 4 to 8 hours and often this issue is ameliorated.
>
> Question 2 - What are the best AR and UR coatings asked by Michael Strong of MG Chemicals�.a competitor to HumiSeal et al so I need to be careful, and please don't complain if this seems too commercial, but since several of you asked...
>
> OK. First up, 1A33 was, to my knowledge - that is bound to be proved wrong - one of the very first single part urethanes rendering the coating process far easier and with less material waste compared to 2 part formulations. Also, it was TDI free.
>
> As for the subject of curing, I would prefer to see the following terms employed in the IPC-CC-830 Standard: Stage 1 = Tack Free; Stage 2 = Dry (for handling) and Stage 3 = Full cure.
>
> The product will reach Tack Free in around 30 to 45 minutes, ambient. Dry in 2 to 4 hours, ambient and full cure either, 12 hour bake at 80C or it will need to be exposed to 80C to initiate the full cure. It is the oil used in the product that turns an amber colour with heat, but that's the trade-off for a more user-friendly product.
>
> 1B31 was first introduced in or around 1975. A single-part acrylic, its main advantage is total repairability. Tack-Free = 10 to 15 minutes ambient; Dry in around 1 hour, ambient and full cure in about 24 hours, ambient.
>
> In around 1979/80, believing that 1B31 represented a major protection breakthrough, I recall being properly admonished by a senior manager at GEC Avionics in Rochester - ENGLAND - that the first conformal coating ever used was a type of Shellac used on the very early radars fitted to various RAF aircraft from around 1942.
>
> So, 1B31 effectively grandfathers ALL acrylic coatings. 1A33 replaced most 2 part urethane formulations. Rather similar to the story of Rolls Royce, they just make a better product and they have a terrific pedigree. They have many worthy competitors.
>
> BTW techies, for those who don't know, I essentially ceased involvement with HumiSeal when I sold my business to them in 2005.
>
> Graham Naisbitt
>
>
> On 15 Feb 2013, at 16:54, Inge Hernefjord <[log in to unmask]> wrote:
>
>> Where is Coating Nosebite....Nicebitt...hm....Naisbitt ?
>>
>> On 15 February 2013 08:14, Michael Strong <[log in to unmask]>wrote:
>>
>>> Just a general query on what are the best AR and UR solvent-based coatings
>>> available.  I know Humiseal and Elantas are big players but I'd like to
>>> know
>>> what are their big products and why.
>>>
>>>
>>>
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