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. >>>> >>>> >>>> >>>> ______________________________**______________________________** >>>> __________ >>>> This email has been scanned by the Symantec Email Security.cloud >>>> service. >>>> For more information please contact helpdesk at x2960 or >>>> [log in to unmask] >>>> ______________________________**______________________________** >>>> __________ >>>> >>>> >>> >>> ______________________________**______________________________** >>> __________ >>> This email has been scanned by the Symantec Email Security.cloud service. >>> For more information please contact helpdesk at x2960 or >>> [log in to unmask] >>> ______________________________**______________________________** >>> __________ >>> >> >> ______________________________**______________________________** >> __________ >> This email has been scanned by the Symantec Email Security.cloud service. >> For more information please contact helpdesk at x2960 or [log in to unmask] >> ______________________________**______________________________** >> __________ >> >> > ______________________________**______________________________**__________ > This email has been scanned by the Symantec Email Security.cloud service. > For more information please contact helpdesk at x2960 or [log in to unmask] > **______________________________**__________ > ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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