CN111787710A - Preparation method of ceramic circuit board - Google Patents

Abstract

The invention provides a preparation method of a ceramic circuit board, wherein the ceramic circuit board comprises a ceramic substrate and a conductive pattern welded on the ceramic substrate through active solder; the preparation method comprises the following steps: s1, providing a metal foil for forming a conductive pattern, and performing thickness reduction treatment on the non-conductive pattern area from the first main surface of the metal foil; s2, arranging an active solder on the ceramic substrate; wherein the active solder is only arranged in the area for connecting the conductive pattern on the ceramic substrate; s3, placing the conductive pattern onto the active filler metal with the ceramic substrate facing the first major surface of the metal foil, and soldering the conductive pattern onto the ceramic substrate through the active filler metal; s4, removing the reduced thickness non-conductive pattern area of step S1 from the second main surface of the metal foil. The invention is beneficial to achieving smaller pattern circuit spacing, does not need etching of active solder, avoids the damage of the active solder etching to the conductive pattern, and improves the pattern precision.

Description

Preparation method of ceramic circuit board

technical field

The invention relates to a preparation method of a ceramic circuit board; more particularly, to a preparation method of an AMB ceramic circuit board.

Background technique

Ceramic circuit boards have the advantages of high thermal conductivity and low expansion. In recent years, they have been more and more widely used in new energy vehicles, power locomotives, aerospace and other fields. Active metal brazing (AMB) connection technology relies on active solder to achieve metallurgical bonding of ceramic substrates and metal conductive lines, and has the advantages of high bonding strength and good reliability of cold and heat cycles.

AMB ceramic circuit boards generally have thicker conductive patterns, and the pattern thickness can reach 0.2 mm or even more than 1 mm. The preparation method of the existing AMB ceramic circuit board is usually to first use the AMB connection technology to weld a whole piece of metal foil to the ceramic substrate, then chemically etch the metal foil to obtain a conductive pattern, and finally use an etching method different from the metal foil etching. The process removes the active solder between the conductive lines, and the etching process of the active solder often requires a long etching time, is costly, and easily damages the conductive lines.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present invention provides a preparation method of a ceramic circuit board, the ceramic circuit board comprises a ceramic substrate and a conductive pattern welded on the ceramic substrate by an active solder; the preparation method comprises the following steps:

S1, providing a metal foil for forming the conductive pattern, and performing a thickness reduction process on the non-conductive pattern area from the first main surface of the metal foil;

S2, disposing active solder on the ceramic substrate; wherein, the active solder is only arranged on the ceramic substrate in the area for connecting the conductive patterns;

S3, with the ceramic substrate facing the first main surface of the metal foil, placing the conductive pattern on the active solder, and soldering the conductive pattern to the ceramic through the active solder on the substrate;

S4, removing the non-conductive pattern region whose thickness is reduced in step S1 from the second main surface of the metal foil.

The sequence of steps S1 and S2 is not limited.

Preferably, the metal foil is copper foil; the thickness of the metal foil is greater than or equal to 0.1 mm and less than or equal to 2 mm.

Preferably, the ceramic substrate is an aluminum nitride or silicon nitride ceramic substrate.

Preferably, conductive patterns are provided on both sides of the ceramic substrate.

In the present invention, in step S1, a method such as mechanical milling, chemical etching or laser ablation can be used to reduce the thickness of the non-conductive pattern area of the metal foil, and in step S4, a method such as mechanical milling, chemical etching or laser ablation can be used. The non-conductive pattern area after the thickness reduction in step S1 is removed. According to a specific embodiment of the present invention, in step S1, a first etching process is used to perform a thickness reduction process on the non-conductive pattern region, and in step S4, a second etching process is used to remove the thickness-reduced part of the non-conductive pattern region in step S1. Non-conductive pattern area.

Preferably, in step S4, the non-conductive pattern region whose thickness is reduced in step S1 is removed by a spray etching process.

More preferably, in step S4, after the metal foil is etched through, the sidewall of the conductive pattern is continuously etched, so as to reduce the protruding copper residue on the sidewall.

According to a specific embodiment of the present invention, in step S1, the thickness of the non-conductive pattern is reduced by 30-80%.

Preferably, in step S1, the thickness of the non-conductive pattern is reduced by 40-70%.

According to a specific embodiment of the present invention, in step S2, active solder is provided on the ceramic substrate by a screen printing process.

In the method for preparing a ceramic circuit board of the present invention, the conductive pattern is produced by performing two-step processing on the metal foil, and the two-step processing is carried out respectively from both surfaces of the metal foil before and after the active solder is welded, so that the active solder can only be arranged on the surface of the metal foil. The area used to connect the conductive patterns on the ceramic substrate reduces the amount of active solder used; the chemical etching step of active solder is not required, the processing time is shortened, chemical pollution is reduced, and the conductive pattern is avoided during chemical etching of active solder. damage and improve graphics accuracy.

In order to illustrate the objectives, technical solutions and advantages of the present invention more clearly, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

Description of drawings

1 is a schematic structural diagram of Embodiment 1 of a ceramic circuit board of the present invention;

2 is a schematic structural diagram of Embodiment 2 of the ceramic circuit board of the present invention;

3 is a flow chart of an embodiment of a method for preparing a ceramic circuit board of the present invention;

4 is a schematic structural diagram of attaching a resist film to the first surface of the metal foil;

5 is a schematic structural diagram of the first surface of the metal foil after etching;

6 is a schematic structural diagram of disposing active solder on the first surface of the ceramic substrate;

7 is a schematic structural diagram of the metal foil after the first etching being welded to the first surface of the ceramic substrate;

8 is a schematic structural diagram of attaching a resist film to the second surface of the metal foil;

FIG. 9 is a schematic view of the structure when the metal foil is etched through the second surface thereof;

FIG. 10 is a schematic view of the structure of the sidewall of the conductive pattern after the protruding copper residues are cut.

Detailed ways

FIG. 1 is a schematic structural diagram of Embodiment 1 of the ceramic circuit board of the present invention. As shown in FIG. 1 , the ceramic circuit board is a single-sided circuit ceramic circuit board, including a ceramic substrate 20 and a conductive pattern 10 . The ceramic substrate 20 has a first surface 21 , and the conductive pattern 10 is connected to the ceramic substrate 20 through the active solder 30 . The first surface 21 is connected by welding. The conductive pattern 10 includes a set of conductive traces 11 with gaps therebetween, such as the gap 12 between the conductive traces 111 and the conductive traces 112 .

FIG. 2 is a schematic structural diagram of Embodiment 2 of the ceramic circuit board of the present invention. As shown in FIG. 2 , the ceramic circuit board of Embodiment 2 is a double-sided circuit ceramic circuit board, including a ceramic substrate 20 , a conductive pattern 10 and a conductive pattern 40 ; wherein, the conductive pattern 10 is welded to the ceramic substrate 20 by an active solder 30 . The first surface 21 of the conductive pattern 40 is welded on the second surface 22 of the ceramic substrate 20 through the active solder 30 . The conductive pattern 10 includes a group of conductive lines 11 with a gap therebetween, and the conductive pattern 40 includes a group of conductive lines 41 with a gap therebetween.

In the embodiment of the present invention, the material of the conductive pattern may be a metal conductive material such as aluminum, copper or its alloy, preferably copper (including pure copper or copper alloy). The thickness of the conductive pattern is preferably 0.1 mm to 2 mm, more preferably 0.2 mm to 1.5 mm, but the present invention is not limited thereto. The conductive pattern 10 and the conductive pattern 40 may have the same or different graphic designs, materials and thicknesses. Usually, the graphic designs of the two are different, but the materials and graphic thicknesses are the same.

In the embodiment of the present invention, the ceramic substrate 20 is preferably an aluminum nitride or silicon nitride ceramic substrate, and its thickness can be selected according to actual needs, preferably 0.2 mm to 2 mm, such as 0.25 mm, 0.635 mm, 1 mm or 1.5 mm , but the present invention is not limited to this.

In the embodiment of the present invention, the active solder 30 can be, for example, silver-copper-titanium active solder, but the present invention is not limited to this, as long as the active solder can realize a reliable connection between the conductive pattern and the ceramic substrate 20, that is, Can.

Hereinafter, embodiments of the preparation method of the ceramic circuit board of the present invention will be described with reference to the accompanying drawings 3-10.

As shown in FIG. 3 , an embodiment of the method for preparing a ceramic circuit board of the present invention includes the step S1 of thinning the non-conductive pattern area from the first surface of the metal foil to a predetermined thickness. In step S1, a metal foil for forming a conductive pattern is provided, and a thickness reduction process is performed on the non-conductive pattern area from the first main surface of the metal foil.

Preferably, the chemical etching method is used to reduce the thickness of the non-conductive pattern region in step S1 , and the copper foil used for forming the conductive pattern 10 is etched and thinned as an example to illustrate. First, as shown in FIG. 4, a copper foil 10' for forming a conductive pattern 10 is provided, and a first resist film RF1 is covered on the first surface 101 of the copper foil 10' corresponding to the area of the conductive pattern 10, that is, a first resist film RF1. The area where the surface 101 is exposed to the resist film RF1 is the non-conductive pattern area of the copper foil 10'.

Then, as shown in FIG. 5, the thickness of the non-conductive pattern area is reduced by a first etching process (such as a spray etching process), and the thickness of the non-conductive pattern area is reduced by 30-80%, preferably 40-70% %, for example, as shown in FIG. 5, the thickness of the non-conductive pattern area is reduced by about 50%, and after the thickness is reduced, a gap groove 121 is formed on the first surface 101 of the copper foil 10'.

In the first etching process of step S1, set the target spacing of the pattern lines (for example, the gap 12 between the conductive lines 111 and the conductive lines 112) as L, the opening spacing of the resist film RF1 as D1, and the etching depth as H1, then Control L=D1+H1.

The embodiment of the method for preparing the ceramic circuit board of the present invention further includes the step S2 of disposing active solder on the area of the ceramic substrate corresponding to the conductive pattern. Wherein, the active solder can be arranged on the ceramic substrate by using a screen printing process, so that the active solder is only arranged on the area of the ceramic substrate for connecting the conductive patterns.

When preparing the single-sided circuit ceramic circuit board shown in FIG. 1 , as shown in FIG. 6 , the active solder 30 can be screen-printed on the first surface 21 of the ceramic substrate 20 corresponding to the area of the conductive pattern 10 . It is easy to understand that when preparing the double-sided circuit ceramic circuit board as shown in FIG. 2 , it is also necessary to screen-print the active solder 30 on the second surface 22 of the ceramic substrate 20 corresponding to the conductive pattern 40 ; wherein, the ceramic substrate The screen printing of the active solder 30 on both surfaces 20 is carried out separately.

The embodiment of the method for preparing the ceramic circuit board of the present invention further includes the step S3 of soldering the conductive pattern area on the first surface of the metal foil to the surface of the ceramic substrate. That is, in step S3, with the ceramic substrate facing the first main surface of the metal foil, the conductive pattern is placed on the active solder, and the conductive pattern is welded to the ceramic substrate through the active solder.

Taking the connection between the conductive pattern 10 and the ceramic substrate 20 as an example, as shown in FIG. 7 , the ceramic substrate 20 faces the first main surface 101 of the copper foil 10' (that is, the second main surface 102 of the copper foil 10' is relatively far away from the ceramic substrate 20 ), place the conductive pattern 10 on the active solder 30 on the first surface 21 of the ceramic substrate 20 , and make the conductive pattern 10 solder to the ceramic substrate 20 through the active solder 30 . Since the various components of the conductive pattern are welded to the ceramic substrate in a state of being connected together in step S3, the relative positions of the various components in the conductive pattern can be accurately determined.

The embodiment of the preparation method of the ceramic circuit board of the present invention further includes step S4: removing the non-conductive pattern area after the thickness reduction in step S1 from the second main surface of the metal foil; Non-conductive pattern area after thickness reduction.

Here, the non-conductive pattern area in the copper foil 10' whose thickness is reduced in step S1 is removed by etching as an example for description. First, as shown in FIG. 8, the area corresponding to the conductive pattern 10 on the second surface 102 of the copper foil 10' is covered with the second resist film RF2, that is, the area where the second surface 101 is exposed to the resist film RF2 is the copper foil The non-conductive pattern area thinned in step S1 in 10'. Then, the thinned non-conductive pattern area in the copper foil 10' is removed by a second etching process, which can also be a spray etching process.

Preferably, in step S4, set the target spacing of the pattern circuit as L, the opening spacing of the resist film RF2 as D2, and the etching depth as H2, then control L>D2+H2. Correspondingly, the spray etching in step S4 is preferably controlled to include two stages: the first stage of etching through the copper foil 10' and the second stage of etching the sidewall of the conductive pattern 10. As shown in FIG. 9, in the first stage of step S4, the copper foil 10' is etched through the second main surface 102 of the copper foil 10', so that the various components of the conductive pattern 10 are separated from each other to form a gap 12, since L> D2+H2, so when the first-stage etching is completed, the pattern line spacing on the second main surface 102 is smaller than the target spacing L; and the sidewall of the conductive pattern 10 has two protruding copper residues 122 caused by etching from different sides , the protruding copper residue 122 usually adversely affects the electrical properties of the ceramic circuit board.

As shown in FIG. 10 , in the second stage of step S4 , that is, after etching through the metal foil 10 ′, the sidewall of the conductive pattern 10 is continuously etched. During this process, the etching rate of the protruding copper residue 122 will be greater than The etching rate of other areas of the sidewall, after a certain period of continuous etching, the pattern line spacing of the second main surface 102 reaches the target spacing, and the protruding copper residue 122 is etched away, so that the sidewall of the conductive pattern 10 is almost vertical, Graphics are more precise.

For the fabrication steps of the conductive pattern 40, reference may be made to the fabrication of the conductive pattern 10 described above, and details are not repeated here.

In the above-mentioned embodiment of the ceramic circuit board preparation method, the metal foil is etched in two times, and the single etching amount is reduced. Compared with the one-time etching in the prior art, the film compensation can be reduced by half. Reduced by half, the minimum pattern spacing is reduced. In particular, the metal foil is etched in two times, and the two etchings are carried out from both surfaces of the metal foil before and after the active solder is welded, so that the active solder can be arranged only on the area of the ceramic substrate for connecting the conductive patterns, The usage amount of active solder is reduced; the chemical etching step of active solder is not required, processing time is shortened, chemical pollution is reduced, damage to conductive patterns during chemical etching of active solder is avoided, and pattern accuracy is improved.

In other preparation method embodiments of the present invention, the thickness reduction treatment in step S1 may also use methods such as mechanical milling or laser ablation to reduce the thickness of the non-conductive pattern area by 30-80%, preferably 40-70% %; Step S4 may also use a metal material removal method such as mechanical milling or laser ablation to remove the non-conductive pattern area after the thickness reduction in step S1.

Although the present invention is disclosed above with specific embodiments, these specific embodiments are not intended to limit the scope of implementation of the present invention. Any person of ordinary skill in the art can make some changes/replacements without departing from the scope of the present invention, that is, any equivalent changes made in accordance with the present invention should be covered by the protection scope of the present invention.

Claims (10)

1. A preparation method of a ceramic circuit board comprises a ceramic substrate and a conductive pattern welded on the ceramic substrate through active solder; the preparation method comprises the following steps:

s1, providing a metal foil for forming the conductive pattern, and performing thickness reduction treatment on a non-conductive pattern area from the first main surface of the metal foil;

s2, arranging an active solder on the ceramic substrate; wherein the active filler metal is provided only on a region of the ceramic substrate for connecting the conductive pattern;

s3, placing the conductive pattern onto the active filler metal with the ceramic substrate facing the first major surface of the metal foil, and soldering the conductive pattern onto the ceramic substrate through the active filler metal;

s4, removing the non-conductive pattern area with the reduced thickness in the step S1 from the second main surface of the metal foil.

2. The production method according to claim 1, wherein the metal foil is a copper foil, and the thickness of the metal foil is 0.1 mm or more and 2 mm or less.

3. The production method according to claim 1, wherein the ceramic substrate is an aluminum nitride or silicon nitride ceramic substrate.

4. The production method according to claim 1, wherein both sides of the ceramic substrate are provided with a conductive pattern.

5. The method of claim 1, wherein: in step S1, the non-conductive pattern region is subjected to a thickness reduction process by a first etching process, and in step S4, the non-conductive pattern region with the reduced thickness in step S1 is removed by a second etching process.

6. The method of claim 5, wherein: in step S4, the non-conductive pattern area with the reduced thickness in step S1 is removed by a spray etching process.

7. The method of claim 6, wherein: in step S4, after etching through the metal foil, the sidewalls of the conductive pattern are continuously etched to reduce the protruding residual copper on the sidewalls.

8. The method of claim 1, wherein: in step S1, the thickness of the non-conductive pattern region is reduced by 30 to 80%.

9. The method of claim 7, wherein: in step S1, the thickness of the non-conductive pattern areas is reduced by 40-70%.

10. The method of claim 1, wherein: in step S2, an active filler metal is provided on the ceramic substrate by a screen printing process.

Images