GB1558748A - Electrical resistor network - Google Patents

Description

(54) ELECTRICAL RESISTOR NETWORK (71) We, WELWYN ELECTRIC LIMITED, of Bedlington, Northumberland NE22 7AA, a British Company, do hereby declare the invention, for which we pray that a patcnt may be granted to us, and the method by which it is to be performed, to be particumarly described in and by the following statement: This invention relates to an electrical resistor ladder network consisting of elec trioally interconnected resistance elements on an electrically insulating substrate.

The present invention provides an electrical resistor ladder network comprising a planar array of electrically interconnected resistance elements on an electrically insulating substrate, said array comprising a series chain of electrically interconnected resistance elements and a plurality of further resistance elements each having an electrical connection to a junction between a separate pair of interconnected elements in said series chain, said series chain of elements and said further elements and interconnections therefor being constituted by a patterned metal foil adhered to said substrate.

It is to be undersbood that in this invention a metal foil is defined as a very thin sheet of metal (the term metal also including metal alloy) capable of existing in its own right without necessity for a supporting substrate and is distinguished from a metal film which is deposited on a substrate and which cannot exist apart from the substrate.

The said patterned metal foil suitably comprises a single sheet of metal foil from which preselected portions have been removed; removal of said preselected portions may suitably have been effected by an etching process, e.g. a mechanical, chemical elieotrochemioal or laser etching process.

A material having higher electrical conductivity than said foil may be provided on seleoted regions of said patterned foil to constitute electrical terminals and /or contacts for said network.

Preferably said foil comprises an alloy containing nickel and chromium as major constituents.

The ladder network may comprise a multi- bit current or voltage ladder network and i.1 one specific embodiment, to be described in detail hereafter, by way of example, could consist of resistance elements of resistance value R and resistance elements of resistance value 2R; the resistance elements R are connected in series and the resistance elements 2R are respectively connected at junctions between adjacent said elements R.

The invention is now described by way of example with reference to the accompanying drawing which illustrates a perspex tive view of a resistor ladder network of the invention.

The resistor network shown in the drawing comprises a metal foil 1, e.g. of nickel chromium alloy, and of typical thickness 3 to 5 microns, adhered to a flat electrically insulating ceramic substrate 2 by means of an adhesive (not shown), a suitable adhesive being an epoxy adhesive, which is well known in the art. The foil 1 is patterned and has provided therein a planar array of eletrically interconnected resistance elements la, lb, Ic, id and le. The interconnected array of foil resistance elements is isolated from the surrounding foil by a continuous gap 3.Terminal pads 4, 5, 6, 7 and 8 are provided comprising regions of foil overlaid with a material having higher eleotricail oonductivity than the foil, gold being padicu- larly suitable for this purpose. The resistance elements la, ib and ic, connected in series each suitably have the same resistance value R and the resistance elements id and 1 e are conneoted at the junctions between elements la and lb and between elements ib and ic, respectively, suitably each have a resistance value 2R.The resulting resistor network is an R-2R ladder network. The series chain of elements la, lib, ic may be extended to include as many elements as desired and further elements in the same manner as id and le may be included connected at junctions between the elements in the series chain.

The resulting network may be provided covering (not shown), e.g. of a lacquer or a suitable encapsulant, such coverings being very well known in the art.

The resistor network shown in the drawing can be produced as follows. An unpatterned sheet of foil 1, e.g. of nickelchromium alloy is adhered to electrically insulating ceramic substrate 2 by means of a suitable adhesive, e.g. an epoxy adhesive.

The foil is then covered with a film of a photoresist material (well known in the art) v.-'1icll is patterned in well known manner so that openings are formed therein to leave exposed a pattern of foil corresponding to the gap 3 which it is desired to produce to isolate the array of foil resistance elements la, ib, Ic, id, le and their terminal pads 4, 5, 6, 7 and 8. The exposed foil is then etched away, using an acid etchant, until the underlying substrate is exposed. The photoresist film is then removed, leaving the array of foil resistance elements la, ib, ic, Id and le, isolated by the gap 3, on the substrate.The entire surface of the foil and also the gap 3 is then coated with a further photoresist film which is patterned so that terminal pads 4, 5, 6, 7 and 8 are exposed. A metal such as gold is then deposited onto the pads through the openings in the photoresist to facilitate the making of electrical connections to the resulting network. The photoresist film is then removed.

WHAT WE CLAIM IS:- 1. An electrical resistor ladder network comprising a planar array of electrically interconnected resistance elements on an electrically insulating substrate, said array comprising a series chain of electrically in terconnected resistance elements and a plurality of further resistance elements each having an electrical connection to a junction between a separate pair of interconnected elements in said series chain, said series chain of elements and said further elements and interconnections therefor being constitutted by a patterned metal foil adhered to said substrate.

2. An electrical resistor ladder network according to Claim 1 in which said patterned metal foil comprises a single sheet of metal foil from which preselected portions have been removed.

3. An electrical resistor ladder network according to Claim 2 in which removal of said preselected portions has been effected by an etching process.

4. An electrical resistor ladder network according to Claim 3 in which a mechanical, chemical, electrochemical or laser etching process has been used to remove said preselected portions.

5. An electrical resistor ladder network according to any one of the preceding claims in which a material having higher electrical conductivity than said foil is provided on selected regions of said patterned foil to constitute electrical terminals and/or contacts for said network.

6. An electrical resistor ladder network according to any one of the preceding claims in which said foil comprises an alloy containing nickel and chromium as major constituents.

7. An electrical resistor ladder network according to any one of the preceding claims, in which said ladder network is a multi-bit current or voltage ladder network.

8. An electrical resistor ladder network according to any one of the preceding claims in which each element in said series chain is of resistance value R and each of said further elements is of resistance value 2R.

9. An electrical resistor ladder network constructed and arranged substantially as herein described and shown in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. suitable encapsulant, such coverings being very well known in the art. The resistor network shown in the drawing can be produced as follows. An unpatterned sheet of foil 1, e.g. of nickelchromium alloy is adhered to electrically insulating ceramic substrate 2 by means of a suitable adhesive, e.g. an epoxy adhesive. The foil is then covered with a film of a photoresist material (well known in the art) v.-'1icll is patterned in well known manner so that openings are formed therein to leave exposed a pattern of foil corresponding to the gap 3 which it is desired to produce to isolate the array of foil resistance elements la, ib, Ic, id, le and their terminal pads 4, 5, 6, 7 and 8. The exposed foil is then etched away, using an acid etchant, until the underlying substrate is exposed. The photoresist film is then removed, leaving the array of foil resistance elements la, ib, ic, Id and le, isolated by the gap 3, on the substrate.The entire surface of the foil and also the gap 3 is then coated with a further photoresist film which is patterned so that terminal pads 4, 5, 6, 7 and 8 are exposed. A metal such as gold is then deposited onto the pads through the openings in the photoresist to facilitate the making of electrical connections to the resulting network. The photoresist film is then removed. WHAT WE CLAIM IS:-

1. An electrical resistor ladder network comprising a planar array of electrically interconnected resistance elements on an electrically insulating substrate, said array comprising a series chain of electrically in terconnected resistance elements and a plurality of further resistance elements each having an electrical connection to a junction between a separate pair of interconnected elements in said series chain, said series chain of elements and said further elements and interconnections therefor being constitutted by a patterned metal foil adhered to said substrate.

2. An electrical resistor ladder network according to Claim 1 in which said patterned metal foil comprises a single sheet of metal foil from which preselected portions have been removed.

3. An electrical resistor ladder network according to Claim 2 in which removal of said preselected portions has been effected by an etching process.

4. An electrical resistor ladder network according to Claim 3 in which a mechanical, chemical, electrochemical or laser etching process has been used to remove said preselected portions.

5. An electrical resistor ladder network according to any one of the preceding claims in which a material having higher electrical conductivity than said foil is provided on selected regions of said patterned foil to constitute electrical terminals and/or contacts for said network.

6. An electrical resistor ladder network according to any one of the preceding claims in which said foil comprises an alloy containing nickel and chromium as major constituents.

7. An electrical resistor ladder network according to any one of the preceding claims, in which said ladder network is a multi-bit current or voltage ladder network.

8. An electrical resistor ladder network according to any one of the preceding claims in which each element in said series chain is of resistance value R and each of said further elements is of resistance value 2R.

9. An electrical resistor ladder network constructed and arranged substantially as herein described and shown in the accompanying drawing.