Method for making a circuit board and article made thereby

Abstract

A circuit board having a photoflash array is provided based on the screen printing of a radiation curable ink onto the surface of a substrate followed by the radiation cure of the ink.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

With further reference to FIG. 1, there is shown a typical circuit board consisting of a substrate at 10 having conductive circuitry exemplified by 11. These conductive circuit elements can be formed on the surface of 10 in accordance with the method of the invention by applying the above described radiation curable ink onto the substrate surface by standard printing or roto-gravure techniques. For example, 100 to 400 mesh stainless steel screen can be used to apply the radiation curable ink to a thickness of 3 to 5 mils on the surface of the substrate in the circuit pattern desired. Suitable substrates include, for example, polystyrene, polycarbonate, polyethylene terephthalate, polypropylene, polyacrylates, etc.

Cure of the radiation curable ink can be achieved with conventional U.V. discharge lamps such as one or more GEH3T7 suitably ballasted to achieve the desired degree of intensity. U.V. radiation having a wavelength of between about 1849 to 4000 A can be used effectively.

In order to insure a cure time of between 1 to 2 minutes or less, it has been found desirable to operate the lamps at a sufficient flux to provide at least 15,000 microwatts of light per sq. cm. The flux can be varied by altering the lamp ballast, the distance from the substrate, etc.

The circuit board of FIG. 2, more particularly shows a circuit board array suitable for a multiple flash unit for sequential firing of flash bulbs consisting of non-conductive substrate at 20, and contact circuitboard

In addition, although ambient cure temperatures provide effective results in the practice of the method of the invention a cure temperature of up to about 60°C is preferred.

It has also been found that the circuit boards made in the practice of the inventions as shown by FIGS. 1-3 can be subjected to a Tropical Humidity Test requiring exposure for 14 days at a temperature of 120° F. and a RH of 96% without any substantial change in either conductivity or switch performance occuring occurring.

Claims

1. A circuit board suitable for activating high voltage flash lamps consisting of a nonconductive substrate having patterned electrically conductive circuitry on its surface at a thickness of up to about 5 mils with a specific resistivity of less than 10 ohm-cm, where said patterned electrically conductive circuitry is comprised of an organic resin matrix and a particulated electrically conductive metal containing material, and which electrically conductive circuit suffers less than a 2% weight loss based on the weight of electrically conductive circuitry when baked for 60 minutes at a temperature of 70°C, where said particulated electrically conductive metal containing material is substantially free of metal containing material having an aspect ratio of diameter to thickness of a value greater than 20.

2. A circuit board in accordance with claim 1, where the non-conductive substrate is a flexible substrate.

3. A circuit board in accordance with claim 2 which is capable of being flexed at least five times to produce an arc having up to a 1 high displacement

without substantially changing its specific resistivity. 4. A circuit board in accordance with claim 1, where the cured blend comprises a reactive product of styrene and polyester as the organic resin matrix and silver coated glass beads as the particulated electrically conductive

metal containing material.

5. A circuit board for a planar flush away in accordance with claim 1, consisting of circuit runs electrically connected to at least one lamp connection area and switching circuitry adjacent said lamp connection area to provide for the sequential flashing of at least two high voltage flashbulbs.

6. A circuit board in accordance with claim 1, where the particulated electrically conductive metal containing material contains up to 15% by weight of silver flake.

. A circuit board which is capable of providing sequential firing of individual high voltage flash lamps in a multiple photo flash array consisting of

A. a flexible non-conductive substrate

B. patterned electrically conductive circuitry on the flexible non-conductive substrate having a specific resistivity of less than 10 ohm-cm and

C. a plurality of radiation switches on the flexible non-conductive substrate,

where the patterened electrically conductive circuitry is patterned on the flexible non-conductive substrate to provide spaced apart electrical circuit board leads and circuit element connecting means to effect sequential firing of high voltage flash lamps and the plurality of radiation switches is patterned as a mass of material adjacent to said circuit element connecting means to receive radiant energy from firing said lamps, where the patterned electrically conductive circuitry is comprised of an organic resin matrix and a particulated electrically conductive metal containing material and is capable of suffering less than 2% weight loss when baked for 60 minutes at a temperature of 70° C., and where said electrically conductive metal containing material is substantially free of metal containing material having an aspect ratio of diameter to thickness of a value greater than 20.

8. A circuit board in accordance with claim 7, which can be repeatedly flexed to an arc displacement of about 1 inch without exhibiting a substantial change in specific resistivity.

9. A circuit board in accordance with claim 7, where the radiation switch comprises a tack-free blend of an organic polymer binder and a mixture of silver oxide and silver carbonate and up to 2% by weight based on the weight based on the weight of the mixture of

benzotriazole. 10. A circuit board which is capable of providing sequential firing of individual high voltage flash lamps in a multiple photo flash array consisting of

A. a polystyrene substrate

B. patterned electrically conductive circuitry on the polystyrene substrate having a specific resistivity of less than 10 ohms-cm, and

C. a plurality of radiation switches on, the polystyrene substrate where the patterned electrically conductive circuitry is patterned on the polystyrene substrate to provide spaced apart electrical circuit board leads to both ends and circuit element connecting means to effect the sequential firing a high voltage flash lamp and the plurality of radiation switches is patterned as a mass of material adjacent to said circuit element connecting means to receive radiant energy from the firing of said flash lamps, where the patterned electrically conductive circuitry is comprised of an organic resin matrix in the form of a reaction product of a polyester and styrene and silver coated glass beads and is cured sufficiently so as to suffer less than 22% 2% weight loss when baked for 60 minutes at 70°C, and the plurality of radiation switches is a mixture of silver oxide and silver carbonate in a matrix of hydroxyethyl cellulose.

11. A circuit board in accordance with claim 10, which is capable of substantially maintaining such specific resistivity after being subjected to a tropical humidity test for two weeks at 120° F. and of a relative humidity of 96%.

12. A circuit board for activating high voltage flash lamps, said circuit board including a non-conductive, thermoplastic substrate having a patterned electrically conductive coating on one of its surfaces and defining electrical circuitry for the flash lamps, said coating having a resistivity of less than 10 ohm-cm and comprising an organic resin matrix which has been cured into a non-tacky condition by ultraviolet radiation, said coating further comprising a particulated electrically conductive material selected from the group consisting of a particulated electrically conductive metal and a particulated electrically conductive metal containing material, including mixtures thereof, with no more than up to about 15% by weight of said particulated electrically conductive material having an aspect ratio of diameter to thickness of a value greater than 20.

13. A circuit board as defined in claim 12 in which at least 85% by weight of said particulated electrically conductive material is constituted by silver-coated glass spheres and in which up to about 15% by weight of said particulated electrically conductive material is constituted by silver flakes having an aspect ratio of diameter to thickness of a value greater than 20.

14. A circuit board for activating high voltage flash lamps, said circuit board including a non-conductive, thermoplastic substrate having a patterned electrically conductive coating on one of its surfaces and defining electrical circuitry for the flash lamps, said coating having a resistivity of less than 10 ohm-cm and comprising an organic resin matrix which has been cured into a non-tacky condition by ultraviolet radiation, at least about 40% and not more than about 90% by weight of said coating being formed by particles bound together by said matrix and having electrically conductive outer surfaces which shield the transmission of ultraviolet radiation through the particles, and at least about 85% by weight of said particles being silver-coated glass spheres having a diameter of between 10 and 50 microns.