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February 2013

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Subject:
From:
Inge Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge Hernefjord <[log in to unmask]>
Date:
Sat, 16 Feb 2013 01:08:57 +0100
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Is shellac still used? / Inge
PS. U worked 1940!!! How old are you, man??? I thought some 70+ but you
must be 70+++

On 16 February 2013 00:41, Brian Ellis <[log in to unmask]> wrote:

> 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]**
>>> com <[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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