Method of manufacture of EMI/RFI vapor deposited composite shielding panel

DETAILED DESCRIPTION The process of this invention can be carried out with existing commercial vapor metalizing equipment.
Preferably such equipment is modified to allow for dual firing of the different metal layers and also the appropriate electrode is provided so that glo-discharge treatment can take place in situ.
Full cycle time for a typical 6 foot diameter by 6 foot long vacuum chamber is about 20 minutes.
EXAMPLE A 12-inch square by 0.
125 inch thick polyphenylene (NORYL) substrate was subjected to glow-discharge cleaning for about 3 minutes in situ in a vacuum metalizing chamber equipped with a dual firing mechanism.
The glow-discharge conditions included an air pressure of 100 to 200 microns of mercury with a plasma voltage of about 1,500 volts, which provided a current of about 200 milliamps.
Immediately after the glow-discharge treatment that provided an active substrate surface, the surface was vapor plated with an adhesive layer of chromium to provide a chromium thickness of about 500 Angstroms.
The pressure within the vessel for all vapor plating was below about 5.
times.
10.
sup.
-5 TORR.
The adhesive chromium layer was next vapor plated with a copper shielding layer to a thickness of about 1,100 Angstroms.
The copper shielding layer was next vapor plated with another chromium layer to form a protective coating.
This protective layer of chromium had a thickness of about 1,000 Angstroms to provide abrasion resistance and to prevent oxidation of the copper shielding layer.
A similar substrate conventionally coated with nickel-acrylic paint to a thickness of 2.
5 mil was utilized as a control for testing.
A comparison of the shielding effectiveness is shown in the table below.

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Shielding Effectiveness in Decibels
Frq.
MHZ 30 60 70 100 300 500 700 1000
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PANEL
Chrome-copper-
30 36 36 40 50 52 51 59
chrome
Nickel-acrylic
22 36 37 46 53 53 53 59
(control 2