The original designation was XP, consisting of kraft paper, impregnated 
with a phenol-formaldehyde resin, not necessarily with the best 
electrical properties, as is was more usually pressed with a decorative 
melamine-impregnated paper sheet ('Formica'). When Pye Radio Ltd, 
Cambridge and Fry's Solders, Mitcham, were co-operating to put the first 
wave soldering machine ("Flowsolder") into production c. 1955, the got 
Formica Ltd to make some rolled copper-clad XP. This was an outstanding 
failure (the copper came off in the solder wave!!). After several 
trials, Formica made an XPC version, with a better electrical and more 
adhesive resin and electrodeposited copper, bought from the Royal Mint 
(electrolytic purification of copper for making bronze coins). This 
worked. Further development produced XXXPC laminate using drum-EDCF 
treated copper, which was the industry standard for most applications 
until the early 1960s. The first epoxy/glass was about 1958, I think, 
but was expensive. It had the designation G-x where x was an integer, 
standardised into G-10 by 1960. FR-4 did not become popular until the 
late 1960s, after the Apollo 1 fire killed 3 astronauts because of fumes 
from G-10 burning in 1967. Electrically and chemically, FR-4 was 
slightly inferior to G-10. The first flame-resistant PF version of XXXPC 
was FR-1, followed by a cheaper FR-2. FR-3 was an epoxy paper, using a 
similar resin mix as FR-4. It was superior to FR-1/2.

AFAIK DH99 is a wood laminate for flooring.

Brian

On 19/06/2012 17:38, Roger M Unwin wrote:
> Hi TechNet,
>
> Does anyone know if DH 99 Bakelite laminate is still available, or what
> a modern equivalent might be ?
>
> The drg that specifies it is dated 1973, and is for an Antenna of some
> type.
>
>
>
> Many Thanks

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