GB1574438A - Printed circuits - Google Patents

Printed circuits Download PDF

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Publication number
GB1574438A
GB1574438A GB2991/76A GB299176A GB1574438A GB 1574438 A GB1574438 A GB 1574438A GB 2991/76 A GB2991/76 A GB 2991/76A GB 299176 A GB299176 A GB 299176A GB 1574438 A GB1574438 A GB 1574438A
Authority
GB
United Kingdom
Prior art keywords
board
printed circuit
conductive strips
paste
resin
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2991/76A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Plessey Co Ltd
Original Assignee
Plessey Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Plessey Co Ltd filed Critical Plessey Co Ltd
Priority to GB2991/76A priority Critical patent/GB1574438A/en
Publication of GB1574438A publication Critical patent/GB1574438A/en
Expired legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/22—Secondary treatment of printed circuits
    • H05K3/24—Reinforcing the conductive pattern
    • H05K3/245—Reinforcing conductive patterns made by printing techniques or by other techniques for applying conductive pastes, inks or powders; Reinforcing other conductive patterns by such techniques
    • H05K3/246—Reinforcing conductive paste, ink or powder patterns by other methods, e.g. by plating
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/09—Use of materials for the conductive, e.g. metallic pattern
    • H05K1/092—Dispersed materials, e.g. conductive pastes or inks
    • H05K1/095—Dispersed materials, e.g. conductive pastes or inks for polymer thick films, i.e. having a permanent organic polymeric binder
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3457—Solder materials or compositions; Methods of application thereof
    • H05K3/3485—Applying solder paste, slurry or powder
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/03—Conductive materials
    • H05K2201/0332—Structure of the conductor
    • H05K2201/0335—Layered conductors or foils
    • H05K2201/0347—Overplating, e.g. for reinforcing conductors or bumps; Plating over filled vias

Description

(54) IMPROVEMENTS RELATING TO PRINTED CIRCUITS (71) We THB PLESSBY COMPANY LIMITED, a British Company of 2/60 Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to printed circuits.
It is known to produce on an insulated board by a silk screen printing technique a plurality of film resistors and associated highly conductive interconnecting strips contiguous with said resistors. Such insulating boards have hitherto been provided on the reverse side with a printed conductor pattern, commonly produced by etching or stamping, which is provided for the connection thereto of other circuit components (e.g.
capacitors, transistors, etc.) on said reverse side of the board and it has additionally been proposed that interconnections between the printed conductor pattern and the silkscreened conductive strips on opposite sides of the board be made by plated-through holes provided in the board.
The present invention seeks inter alia to simplify the construction of printed circuits of the general form defined above with significant cost savings, by providing a printed circuit comprising a number of highly conductive strips formed on an insulating surface by applying to predetermined areas on said surface a paste material embodying base metal particles in powder or flake form and plating the deposited material with metal by an electroless plating operation.
Dv means of the present invention the need for providing a printed conductor pattern on the reverse side of a board as described above to which components will be soldered and for providing interconnections between the printed conductor pattern and high conductive strips by plated-through holes is obviated since direct solder connections may be made between the conductive strips and the leads of components conveniently mounted on the other side of the board, the component leads simply extending through holes which may be provided at suitable points in the board.
In one mode of carrying out the present invention the highly conductive strips may be applied to one side of the board by means of a silk screen process using for example a paste of copper particle laden thermosetting resin. The copper particles may comprise copper flakes which provide small surface irregularities on the conductive strips. After curing of the paste material by passing the board through an oven the copper strips may be plated with a more noble metal by means of the electroless plating operation.
For example, the copper strips may have applied to them silver cyanide solution to plate the strips with silver to which connecting wires may subsequently be soldered.
It should be understood that other materials than copper may be used as the base material for the highly conductive connecting strips.
For instance tin or nickel may be used but again the particles of these metals will be selected to provide the requisite surface irregularities to facilitate soldering. As in the case of copper when tin or nickel is used it will be plated with a more noble metal than itself in order to effect electroless plating.
According to another mode of carrying out the present invention the highly conductive strips may be applied in the form of a paste comprising a base metal powder or flakes such as of aluminium tin or solder alloy dispersed in a thermosetting resin together with noble metal powder or flakes typically comprising 10% of the total metal weight.
The metal powders or flakes may be of any commercially available form (e.g. spherical flake) and preferably having a particle size less than 15 microns across the major dimension.
The paste which may be applied to an insulating board (e.g. phenolic, epoxy or melamine sheet) by screen printing or spraying may be prepared by ball and roll milling and resin solvent, such as benzyl alcohol or ethylene glycol monoethyl ether, added to adjust the viscosity of the paste to the requisite level for applying the paste to the board.
After application of the paste to the board the board may be heated to a temperature of about 1500 for a time to produce a partial cure of the resin. After cooling the board is then immersed in an electroless plating bath to plate the highly conductive strips with copper or other metal to improve solderability. The board may then be washed and again heated to complete the cure of the thermosetting resin. The plating of the partially cured metal laden resin gives better adhesion between the copper plate and the metal laden resin.
It is also contemplated that the highly conductive strips may advantageously be provided with overlying pads of solder paste also conveniently applied by the silk screening technique.
Film resistors may also be applied to the board by silk screening so that the highly conductive strips are contiguous therewith.
These resistors may be put down as a mixture of phenolic resin and benzyl alcohol with carbon black and possibly silver powder added to provide the requisite resistance value. After silk screening the board will be passed through an oven to drive off the benzyl alcohol.
In order to protect the film resistors in cases where wave soldering is to be used for connecting the component leads to the conductive strips selected areas of the board including the film resistors and parts of the conductive strips may be coated with an insulating varnish, such as polyimide, which is chemically stable and extremely resistant to solvent attack.
The holes in the board for receiving the connecting leads of the components which will be mounted on the reverse side of the board to that carrying the film resistors and highly conductive strips may be drilled before or after the film resistors and conductive strips are applied to the board.
WHAT WE CLAIM IS: 1. A printed circuit comprising a number of highly conductive strips formed on an insulating surface by applying to predetermined areas on said surface a paste material embodying base metal particles in powder or flake form and subsequently plating the deposited material with metal by an electroless plating operation.
2. A printed circuit as claimed in claim 1, in which the base metal particles comprise aluminium, tin or a solder alloy.
3. A printed circuit as claimed in claim 1 or claim 2, in which the paste material includes noble metal particles.
4. A printed circuit as claimed in claim 3, in which the noble metal particles are silver.
5. A printed circuit as claimed in any one of claims 1 to 4, in which the paste material is plated with copper.
6. A printed circuit as claimed in claim 1, in which the paste material comprises copper flakes or powder in a thermosetting resin.
7. A printed circuit as claimed in claim 1, in which the paste material comprises tine or nickel powder or flakes in thermosetting resin.
8. A printed circuit as claimed in claim 6 or claim 7, in which the paste material after curing is plated with a noble metal (e.g. silver).
9. A printed circuit as claimed in any preceding claim, in which the insulating surface is defined by one side of an insulating board.
10. A printed circuit board produced substantially as hereinbefore described.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. less than 15 microns across the major dimension. The paste which may be applied to an insulating board (e.g. phenolic, epoxy or melamine sheet) by screen printing or spraying may be prepared by ball and roll milling and resin solvent, such as benzyl alcohol or ethylene glycol monoethyl ether, added to adjust the viscosity of the paste to the requisite level for applying the paste to the board. After application of the paste to the board the board may be heated to a temperature of about 1500 for a time to produce a partial cure of the resin. After cooling the board is then immersed in an electroless plating bath to plate the highly conductive strips with copper or other metal to improve solderability. The board may then be washed and again heated to complete the cure of the thermosetting resin. The plating of the partially cured metal laden resin gives better adhesion between the copper plate and the metal laden resin. It is also contemplated that the highly conductive strips may advantageously be provided with overlying pads of solder paste also conveniently applied by the silk screening technique. Film resistors may also be applied to the board by silk screening so that the highly conductive strips are contiguous therewith. These resistors may be put down as a mixture of phenolic resin and benzyl alcohol with carbon black and possibly silver powder added to provide the requisite resistance value. After silk screening the board will be passed through an oven to drive off the benzyl alcohol. In order to protect the film resistors in cases where wave soldering is to be used for connecting the component leads to the conductive strips selected areas of the board including the film resistors and parts of the conductive strips may be coated with an insulating varnish, such as polyimide, which is chemically stable and extremely resistant to solvent attack. The holes in the board for receiving the connecting leads of the components which will be mounted on the reverse side of the board to that carrying the film resistors and highly conductive strips may be drilled before or after the film resistors and conductive strips are applied to the board. WHAT WE CLAIM IS:
1. A printed circuit comprising a number of highly conductive strips formed on an insulating surface by applying to predetermined areas on said surface a paste material embodying base metal particles in powder or flake form and subsequently plating the deposited material with metal by an electroless plating operation.
2. A printed circuit as claimed in claim 1, in which the base metal particles comprise aluminium, tin or a solder alloy.
3. A printed circuit as claimed in claim 1 or claim 2, in which the paste material includes noble metal particles.
4. A printed circuit as claimed in claim 3, in which the noble metal particles are silver.
5. A printed circuit as claimed in any one of claims 1 to 4, in which the paste material is plated with copper.
6. A printed circuit as claimed in claim 1, in which the paste material comprises copper flakes or powder in a thermosetting resin.
7. A printed circuit as claimed in claim 1, in which the paste material comprises tine or nickel powder or flakes in thermosetting resin.
8. A printed circuit as claimed in claim 6 or claim 7, in which the paste material after curing is plated with a noble metal (e.g. silver).
9. A printed circuit as claimed in any preceding claim, in which the insulating surface is defined by one side of an insulating board.
10. A printed circuit board produced substantially as hereinbefore described.
GB2991/76A 1977-04-18 1977-04-18 Printed circuits Expired GB1574438A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB2991/76A GB1574438A (en) 1977-04-18 1977-04-18 Printed circuits

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2991/76A GB1574438A (en) 1977-04-18 1977-04-18 Printed circuits

Publications (1)

Publication Number Publication Date
GB1574438A true GB1574438A (en) 1980-09-10

Family

ID=9749869

Family Applications (1)

Application Number Title Priority Date Filing Date
GB2991/76A Expired GB1574438A (en) 1977-04-18 1977-04-18 Printed circuits

Country Status (1)

Country Link
GB (1) GB1574438A (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2172436A (en) * 1985-03-16 1986-09-17 Marconi Electronic Devices Printed circuits
GB2172438A (en) * 1985-03-16 1986-09-17 Marconi Electronic Devices Printed circuits
GB2172437A (en) * 1985-03-16 1986-09-17 Marconi Electronic Devices Printed circuits
EP0195611A2 (en) * 1985-03-16 1986-09-24 Marconi Electronic Devices Limited Printed electrical circuit and method of connecting components therewith

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2172436A (en) * 1985-03-16 1986-09-17 Marconi Electronic Devices Printed circuits
GB2172438A (en) * 1985-03-16 1986-09-17 Marconi Electronic Devices Printed circuits
GB2172437A (en) * 1985-03-16 1986-09-17 Marconi Electronic Devices Printed circuits
EP0195611A2 (en) * 1985-03-16 1986-09-24 Marconi Electronic Devices Limited Printed electrical circuit and method of connecting components therewith
EP0195612A2 (en) * 1985-03-16 1986-09-24 Marconi Electronic Devices Limited Printed circuit arrangement
EP0199450A2 (en) * 1985-03-16 1986-10-29 Marconi Electronic Devices Limited Printed electrical circuit
EP0203680A2 (en) * 1985-03-16 1986-12-03 Marconi Electronic Devices Limited Electrical device including a printed circuit
EP0203680A3 (en) * 1985-03-16 1987-09-02 Marconi Electronic Devices Limited Electrical device including a printed circuit
EP0199450A3 (en) * 1985-03-16 1987-09-02 Marconi Electronic Devices Limited Printed electrical circuit
EP0195611A3 (en) * 1985-03-16 1987-09-16 Marconi Electronic Devices Limited Printed electrical circuit and method of connecting components therewith
EP0195612A3 (en) * 1985-03-16 1987-09-16 Marconi Electronic Devices Limited Printed circuit arrangement
GB2172436B (en) * 1985-03-16 1989-06-21 Marconi Electronic Devices Electrical circuit

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Legal Events

Date Code Title Description
PS Patent sealed
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee