WO2007042068A1

WO2007042068A1 - Method to manufacture a printed circuit partially protected by an insulating layer

Info

Publication number: WO2007042068A1
Application number: PCT/EP2005/012723
Authority: WO
Inventors: Séverine DIEU-GOMONT; Yannick De Maquille; Jean-Pierre Radenne
Original assignee: Fci
Priority date: 2005-10-11
Filing date: 2005-10-11
Publication date: 2007-04-19

Abstract

The invention relates to a method of making a printed circuit (50), said printed circuit comprising a pattern of first parts (2, 2') and a pattern of second parts (1), the method comprising the steps of providing a dielectric substrate (10); forming on said substrate a metallic layer (12); printing on said metallic layer a first pattern matching the pattern of second parts using a first resist (A), said first resist resistant to a stripper solution (C); printing on said metallic layer a second pattern matching the pattern of first parts using a second resist (B), said second resist being strippable by said stripper solution; etching the metallic layer free of either said first and second resists; stripping said second resist using said stripper solution, while keeping said first resist as an electrical insulation layer. The invention also relates to the printed circuit (50) obtained therewith.

Description

METHOD TO MANUFACTURE A PRINTED CIRCUIT PARTIALLY PROTECTED BY AN INSULATING LAYER

The present invention generally relates to manufacturing methods of printed circuits, and more specifically to a method to manufacture a printed circuit using etching techniques.

Printed circuit can be made using several well known techniques among which one can find printing and etching. Etching consists in laying a metallic layer over a dielectric substrate. A resist is then printed over the metallic layer according to a pattern corresponding to, i.e. matching, the desired printed circuit pattern. The excess metallic layer, i.e. the metal not covered by the resist or the exposed metallic layer, is removed using chemical or electrolytic baths. This step is then followed by the stripping (removal) of the remaining resist to uncover the desired printed circuit pattern.

Planar antennas, as the ones used in an RFID antenna (Radio

Frequency IDentifier), are common examples of printed circuits. They generally comprise a plurality of turns that spiral around on a planar dielectric substrate as seen on FIG. 1 , and antenna terminals 2 and 2' to which a chip can be connected (not represented on FIG. 1 ).

For the antenna patterns that require more than one turn as seen on FIG. 1 , an electrical bridge must be formed over the spiral turns of the antenna to connect the chip contact ends to the antenna terminals 2 and 2' located on opposite side of the antenna tracks 1 (i.e. inside and outside the antenna turns). The bridge must be separated from the antenna turns it crosses over through an insulating layer so as to avoid any short circuit of the antenna.

One known technique is to print a dielectric layer on top of the antenna tracks in between the antenna terminals. Thus the chip can be laid over and attached to the dielectric layer, the chip itself being used as the bridge. In an alternate solution, a metallic bridge can also be printed over the dielectric layer to connect a first terminal on one side of the tracks to a new terminal on the other side of the antenna tracks, new terminal that is next to the second terminal of the antenna. Then a classic bounding technology can be used to attach the chip. Nevertheless such techniques still require a separate and additional step to print the dielectric layer over the antenna turns in the region of the bridge.

JP2001143037 describes an antenna printed circuit that is formed using an etching technique, a step of the method consisting in selectively removing the resist on the parts of the antenna pattern that correspond to the terminals, while keeping the resist on the remaining parts of the antenna as an insulation layer. If this method appears as an effective method, the selective removal of the resist is still separated from the etching process.

The purpose of the present invention is to provide a simple, yet efficient, technique to selectively insulate second parts or non active parts of a printed circuit, while leaving free of any insulation layer its first parts or active parts.

Accordingly, the present invention provides a manufacturing method according to claim 1. The present invention further provides a printed circuit according to claim 12.

The invention takes advantage of the stripper solution which is adapted to solely remove the second resist, while keeping the first resist as an electrical insulation layer. Such layer can later on be used, in the case of a printed antenna circuit for example, to electrically isolate the antenna turns from a bridge crossing over said antenna turns. Furthermore, the method according to the invention offers a fully integrated manufacturing method consistent with the steps of the etching manufacturing method. No additional step apart from the known steps of the etching method is necessary. The first resist layer can also be used as an external protection for the second parts or non active parts. Other features and advantages of this invention will further appear in the hereafter description when considered in connection to the accompanying drawings, wherein:

FIG. 1 illustrates a view of a printed circuit in the form of an antenna in accordance with an exemplary embodiment of the present invention; FIGS. 2.1-2.3 illustrate the different steps of the method according to the invention, according to a section view II.1-11.1.

An exemplary printed circuit 50, of the form of an antenna pattern, is presented on FIG. 1. The following illustration will be based on the antenna circuit of FIG. 1 , but the method according to the invention can also be generalized to any printed circuit using an etching manufacturing method.

Such a printed circuit generally comprises a pattern of first parts or active parts 2 and 2', here the antenna terminals 2 and 2', and a pattern of second parts or non active parts, here the antenna turns 1 , also called later on the antenna tracks. By active parts, one refers for example to any parts of the printed circuit patterns, such as terminals, that are to be connected to external devices such as resistors, capacitances, inductances, chips or any other integrated circuits. Preferably, these active parts are not protected by any insulation layers. The non active parts refer to the printed circuit tracks that electrically connect the active parts to each others, such as, for example, the antenna turns 1 in FIG. 1.

In order to manufacture the printed circuit according to the invention, an etching technique is used and described here after. FIGS. 2.1 to 2.3 illustrate such a manufacturing method.

In a first step of the method according to the invention, a dielectric substrate 10, preferably a planar substrate, is provided. This substrate can be made for example from a polyester film, such as a PET film (polyethylene terephthalate) or a PEN film (polyethylene naphthalate), from polyimides, from epoxy-glass, from PVC. Substrates such as paper can also be used. The substrate can be rigid as well as flexible.

In a second step, a metallic layer 12 is formed on the substrate 10. The metallic layer can be made of copper, aluminum, brass, tin, silver or any other suitable conductive metal or alloy for a printed circuit. The metallic layer can be laminated over the substrate 10 using an adhesive laid over the substrate beforehand if necessary. The thickness of the metallic layer 12 is generally in the 9 to 35mm range, but can also be thinner or thicker depending on the printed circuit specifications.

In a third step, a first pattern matching the targeted pattern of non active parts is printed on the metallic layer using a first resist A. As explained before, a stripper solution is generally used when etching a printed circuit to strip the resist off the etched printed circuit pattern. As the resist A is used as an insulation layer over the non active parts of the printed circuit, the stripper solution used later on in the manufacturing method according to the invention is chosen so that it cannot strip the first resist A off the metallic layer. Therefore, the first resist A is resistant to the chosen stripper solution. Furthermore, resist A is chosen non conductive to provide electrical insulation of the non active parts. To improve insulation from resist A, a second layer of resist A can be deposited over the first layer of resist A. Thus, a sufficient thickness of resist A is obtained with the resulting electrical insulating properties.

In a fourth step of the method according to the invention, a second pattern matching the targeted pattern of active parts is printed on the metallic layer 12 using a second resist B. As the second resist B is to be removed later on, the chosen stripper solution is such that it can strip off the resist B to leave the active parts pattern free of any insulation layer.

Any printing technology can be used to print the pattern of active and non active parts respectively with the first and second resists. Serigraphy, rotogravure, photogravure, lithogravure ... may be used to print these patterns. The third and fourth steps of the method according to the invention may be switched or substantially simultaneously executed if appropriate. Furthermore, in order to improve adhesion of the resist layers A and B, a preliminary surface treatment can be executed on the metallic layer 12 to promote adhesion of the resist layers. Among possible treatments are for example micro etching, degreasing, organic or mineral passivation.

In a fifth step of the manufacturing method according to the invention, the metallic layer 12 free of resists A and B, i.e. the exposed metallic layer, is etched using an etching solution. Thus the parts that are not printed over with the different resists are etched from the substrate, leaving the dielectric substrate 10 free of metal in the unprinted regions. As well known in etching techniques, the metallic layer protected with the resist layers A and B is not responsive to the etching solution.

In a sixth step according to the invention, the second resist B is stripped using the stripper solution. Considering the stripper solution characteristics mentioned here before with regard to resists A and B, the second resist B is removed from the pattern of active parts, leaving said active parts free of resist. Furthermore, the first resist A is kept over the non active parts as an electrical insulation layer, as resist A is a non conductive resist.

Among known resists, resist A can be a resin, an ink or a mixing of different inks and/or resins from the chemical families comprising the mono or dual component polyurethanes, thermally or UV curable epoxy resin, acrylic or methacrylic hydroxylated or carboxylated resins, UV curable acrylic resins, acrylic-styrene copolymers, phenolic resins, formo-phenolic resins, or novolaque resins. Furthermore, resist A should be non conductive. Examples of such resist A known by their brand names are acrylic resins Dianal" BR83 or Dianal^® BR106, ink Suncook^® 1236A or Elvacite^® 2896.

Resist B can be a resin, an ink or a mixing of different inks and/or resins from the chemical families comprising the mono or dual component polyurethanes, acrylic or methacrylic hydroxylated or carboxylated resins, UV curable acrylic resins, maleic anhydrous styrene copolymers, methacrylic methyl-acid methacrylate copolymers, styrene acrylic copolymers, formo- phenolic resins, or novolaque resins. Examples of such resist B known by their brand names are Taiyo Ink^® AS500-LY, ink Electra^® ETAV 24, resin SMA^®

1440F, resin Joncryl^® 678, Alnovol^® PN 160.

Regarding the stripper solution, an alkaline aqueous solution or a solvent from the ketone, alcohol or ester families can be used. An aqueous example of stripper may be a 2% sodium hydroxide or potash solution. An example of a solvent stripper may be a acetone, methyl ethyl ketone, ethyl acetate or ethyl alcohol.

The possibilities of choices are numerous. Nevertheless it remains essential for the method according to the invention that resists A and B, as well as stripper solution, are chosen so that solution can strip resists B but cannot strip resist A. Any couple of resists (A, B) can be chosen among the list of possible resists mentioned here before, provided that a stripper solution that can both: - strip the second pattern printed with resist B,

- while not stripping the first pattern printed with resist A, can be found.

Claims

1. A method of making a printed circuit (50), said printed circuit comprising a pattern of first parts (2, 2') and a pattern of second parts (1 ), the method comprising the steps of: a) providing a dielectric substrate (10); b) forming on said substrate a metallic layer (12); c) printing on said metallic layer a first pattern matching the pattern of second parts using a first resist (A), said first resist being non conductive and resistant to a stripper solution (C); d) printing on said metallic layer a second pattern matching the pattern of first parts using a second resist (B), said second resist being strippable by said stripper solution; e) etching the metallic layer free of either said first and second resists; f) stripping said second resist using said stripper solution, while keeping said first resist as an electrical insulation layer.

2. A method according to the previous claim, wherein step d) is executed before step c) or at least substantially simultaneously.

3. A method according to any one of the previous claims, wherein the first parts comprise circuit terminals (2, 2'), and the second parts comprise circuit tracks (1).

4. A method according to any one of the previous claims, wherein the first resist is a resin, an ink or a mixing of different inks and/or resins.

5. A method according to any one of the previous claims, wherein the first resist is chosen from the chemical families comprising the mono or dual component polyurethanes, thermally or UV curable epoxy resin, acrylic or methacrylic hydroxylated or carboxylated resins, UV curable acrylic resins, acrylic-styrene copolymers, phenolic resins, formo-phenolic resins, or novolaque resins.

6. A method according to any one of the previous claims, wherein the second resist is wherein the first resist is a resin, an ink or a mixing of different inks and/or resins.

7. A method according to any one of the previous claims, wherein the second resist is chosen from comprising the mono or dual component polyurethanes, acrylic or methacrylic hydroxylated or carboxylated resins, UV curable acrylic resins, maleic anhydrous styrene copolymers, methacrylic methyl-acid methacrylate copolymers, styrene acrylic copolymers, formo- phenolic resins, or novolaque resins.

8. A method according to any one*"of the*"previous claims, wherein the stripper solution is an alkaline aqueous solution.

9. A method according to the previous claim, wherein the stripper solution is a sodium hydroxide or potash solution of a few percentages.

10. A method according to any one of the claims 1 to 7, wherein the stripper solution is a solvent from the ketone, alcohol or ester families.

11. A method according to the previous claim, wherein the solvent is an acetone, a methyl ethyl ketone, an ethyl acetate or an ethyl alcohol.

12. A printed circuit (50) comprising:

- a dielectric substrate (10),

- a pattern of first parts (2, 2'), said first parts being free of any insulation layer,

- a pattern of second parts (1 ), said second parts being covered by an insulation layer (A), said printed circuit being made according to the method of claims 1 to 11.