DE4004844C1 - Copper metallisation on ceramic substrate - obtd. by bonding copper foil directly to whole surface of substrate, then masking and etching - Google Patents

Abstract

Structured Cu metallisation is produced on a ceramic substrate by a process in which a Cu foil is bonded directly to the whole surface of the substrate and is then masked and etched. Control of the masking and etching process produces one or all of the forms: (a) rounding of the corners of the metallisation; (b) an edge region of reduced thickness; (c) formation of tooth or finger-shaped edges; (d) sub-division or weakening e.g. by formation of holes in the metallisation. ADVANTAGE - Reduced tendency to crack formation.

Description

The invention relates to a method for Her structured copper metallization a ceramic substrate according to the preamble of the claim 1.

A method of connecting a copper foil directly with a ceramic substrate is from DE-A 32 04 167 known. In the essay "New Power Semiconductor Mod le with high fatigue strength, "BBC News, Volume 64, Issue 7, 1982, pages 196 to 200 is on Page 199 stated that in such a way with a Copper metallization provided substrate by after slow etching can be structured. The second Side of the ceramic substrate can then with a full-surface copper metallization also after Direct connection process to be metallized. Alterna This can also be done with a single bonding process  a copper foil is applied to both sides and then be etched, as in connection technology in electronics nik, VTE 1/89, pages 16 to 19 on page 16 is. In addition, one can, for example, by stamping or etching pre-structured copper foil on the ceramic be applied.

Many have direct-bonded ceramic-copper substrates excellent properties, in particular they exhibit a very adhesive connection between the ceramic plate te and the copper foil. That applies at least to the Connection of an oxide ceramic, e.g. Aluminum moxide with copper. From the company publication "High Ther times Conductivity ALN Substrates "from Toshiba, Serial No. D-62002, dated February 28, 1987 are also direct borrowed dete substrates known, which are based on a non-oxide ceramics, namely aluminum nitride represents are. To such a ceramic with a copper foil To be able to connect directly, the ceramic must surface oxidized. Such a thin oxide layer can only be very limited by different mechani tensions at the transition point from a metal generated to a non-metallized surface Absorb forces. For this reason, he point to the market modules with ALN-insulated substrates tallization with bevelled edges. The abge slanted edges result in a smaller gradient the mechanical stresses at the edge of the metallization surfaces. The metallization of these ALN modules is complete Bonding of pre-structured copper foils. The necessary structuring and chamfering of the Copper foil before bonding requires two etching steps and is therefore complex and leads to a little flexi blen manufacturing. Handling the delicate struk tured copper foils is difficult.  

In VTE 1/89 it is reported on page 19 that even with oxidic ceramics, cracks can occur in the ceramics after exposure to temperature changes, which lead to a so-called shell break. Such crack formation can be prevented by using a high-strength ceramic with a fine particle size distribution. Such ceramics with, for example, 99.5% Al ₂ O ₃ and a bending strength of about 500 MPa are known from thin-film technology. However, like other even firmer ceramics with a dense structure, they are too expensive for the intended mass production and for use in power semiconductor modules.

Another way to reduce the risk The formation of cracks consists in thinning copper foils use, but there are also difficulties surrender. On the structured top of a sub strats you want the thickest possible copper foil in the back have a view of the transverse conductivity. On the Untersei te, the copper foil should also be thick to a to achieve high compressive stress. One different thick metallization should be with regard to one then adjusting curvature can be avoided. Besides, is storage of foils of different thicknesses dig.

That from the production of substrates with nonoxidi known ceramics, namely vorstruktu foils with bevelled edges in the edge area use is because of the difficult handling of the Fo lien also unsatisfactory.

The invention has for its object one from called BBC News known process to manufacture position of a copper metallization on a ceramic To improve the substrate so that afterwards provided products with a significantly lower tendency to Have cracks.

This task is accomplished through a manufacturing process a structured copper metallization on a Ke loosened ceramic substrate, initially with a full-surface Copper layer by connecting a copper foil to the Ceramic substrate using a direct connection process is produced and then by masking and Etching the copper layer the structured copper metalli sation is produced, and by appropriate Masking and a corresponding control of the Ätzpro zesses using the structured metallization one of the design options listed below or any combination thereof is:

• a) rounding corners of the copper metallization,
• b) production of an edge region of the metallization with reduced layer thickness,
• c) fraying the edges of the metallization and
• d) Outline or partial weakening of individuals Areas of structured metallization.

Through these measures, greater pressure and tension can be achieved Differences in the transition from metallized to unmetallized substrate surfaces avoided.

Advantageous refinements are set out in the subclaims given.  

The invention has the advantage that despite the use a copper foil in the usual thickness of about 0.2 to 05 mm, typically 0.3 mm thick, which is on both sides of the Ke ceramic substrate can be applied, cracks in the Ceramics can be avoided. This is done through measures at Masking and etching the already bonded and too struc turizing metallization achieved, so practical no additional effort and handling problems a structured copper foil can be avoided.

Based on the knowledge that cracks in the ceramic arise from the fact that in the etched ceramic area Chen tensile stresses exist while the ceramic areas are under the copper foils under compressive stress through various measures, either individually or in Combination can be applied to decrease of the voltage change gradient at the transition from metal led to non-metallized surfaces. All of these measures only require one appropriate masking and, if necessary, control of the etching process.

Pro produced by the method according to the invention Products are particularly insensitive to local ones short-term high thermal loads, e.g. due to high impulse loads of power semiconductors chips can occur.

A more detailed description of the invention follows from execution example shown in the drawing len.

Show it:

Fig. 1 is a Herge according to the prior art presented structured metallization on a ceramic substrate,

Fig. 2 and 3, a metallization prepared by the process of this invention on a ceramic substrate,

Fig. 4 and 5, a variant of the inventive Her position of Metallisierungskanten,

Fig. 6 to 9 shows a further variant for the production of Metallisierungskanten,

Fig. 10 to 12 variants to structure or weakening of metallizations.

In Fig. 1, a part of a ceramic substrate 1 with egg ner structured copper metallization 2 is shown. The ceramic substrate 1 usually consists of a standard material with 96% Al ₂ O ₃ , which has a bending strength of approximately 280 MPa and is used in thick-film technology. The copper metallization is produced by directly connecting a copper foil, for example 0.3 mm thick, and then etching. This manufacturing method known from the prior art produces steep flanks at the edge of the copper metallization. Arrows indicate that the metallized surfaces of the ceramic are under compressive stress, where there is a vectorial addition of two compressive stresses, while the ceramic is under tensile stress outside of these surfaces. After a typical temperature change load of, for example, ten changes between -40 ° C. and + 125 ° C. with a dwell time of 1 hour each, cracks can occur in a product shown in FIG 3 arise in the Kera miksubstrat 1 . Because of the resultant compressive stress vector mentioned, typical cracks 3 run obliquely to outer metallization corners. Inner corners, on the other hand, are not critical with regard to crack formation.

Fig. 2 shows measures according to the invention for avoiding cracks or cracks in the ceramic, namely a rounding of corners on the copper layer 2 and a bevel from the edges of the copper layer 2 . At the rounded corners 4 and beveled edges 5 , the transition from tensile stress to compressive stress is distributed over a larger area and the grain serves to reduce the change in stress. A cutting plane AB entered in FIG. 2 is shown in FIG. 3, wherein it can be seen that the ceramic substrate 1 has a structured copper metallization 2 on the top and a continuous copper metallization on the bottom. A known screen printing technique or photo mask technique can be used in all proposed procedural variants. The bevelled edges 5 should be at least as wide as they are high in order to achieve the desired effect. A two-stage etching process may be required for particularly flat etchings. FIGS. 4 and 5 show a method using a single etching step len a size ren thinned edge region of the metallization herzustel. Here, Fig. 4 shows a mask 6 which covers a to be patterned copper layer 2. Fig. 5 shows a product after carrying out the etching process in which a ceramic substrate 1 is shown with a struc tured by etching the copper layer 2. It should be known that a wide edge region 7 has arisen, which is not continuously beveled, which is not important here, but is almost uniformly thin compared to the rest of the metallization. The outermost edge area, which was covered by a narrow strip of the mask, has also become thinner as a result of the known undercut effect.

Fig. 6 shows a further measure to avoid cracking, wherein instead of straight edges of Me tallization by fraying elongated edges are struck before, which can be achieved for example by sawtooth or meandering edge shapes. Metallization fingers 8 produced in this way should be dimensioned such that they can still be safely controlled with the respective masking technology. This means, for example, with approximately 0.3 mm thick copper layers that the fingers 8 at their roots 9 should not be less than 1 mm wide and the distances between the fingers 8 should be at least 0.5 mm. From the stand can decrease towards the root 9 , a resulting lower etching is desirable because then a beveled edge is formed. The suggestion for the finger structure can also be expressed as follows: the width and length of the fingers should correspond to approximately three times the thickness of the copper layer and the distances from approximately twice the thickness of the layer. The fingertips are appropriately rounded to avoid voltage peaks.

The measure for edge extension shown in FIG. 6 is proposed in particular for those cases in which a chip with a particularly high pulse load, for example a thyristor under surge current load, is to be arranged on a soldering surface 10 . In other cases, an extension of the edge in the area of corners of the metallization may suffice, as shown in FIG. 10. There are 2 slots 11 made by etching at the corners of the metallization, which extend at an angle of about 45 ° to the inside. Their width is two to three times, their length at least three times the thickness of the copper layer.

In Fig. 6 a sawtooth 12 in addition to a meandering shape with edge fingers 8 is shown. This sawtooth structure 12 is shown enlarged in FIG. 7, with triangular teeth with approximately the same side length being present in the example shown. The side length should be about three times as large as the copper layer thickness. Depending on the available space and given thermal shock load, other triangular shapes, for example with a greater height, can also be provided. When etching the sawtooth structure, the narrow spaces between the triangles are less etched through and the tips are rounded. This is illustrated in the drawing by a section CD entered in FIG. 7, which is shown in FIG. 8, and by a section EF, entered in FIG. 7, which is shown in FIG. 9. It should be noted that the full-area copper layer shown in FIGS . 3, 8 and 9 on the underside of the ceramic substrate does not require any etching treatment, since the ceramic is under compressive stress everywhere.

Another alternative measure is shown in FIGS. 11 and 12. According to this proposal, larger differences in pressure and tensile stress are avoided by a fine structure or a weakening of the copper metallization.

A first variant for implementing this measure is shown in FIG. 11. Fig. 11 shows a ceramic substrate 1 with a copper metallization 2 with a connection area 13 in which a gate connection is to be introduced. To structure or weaken the metallization 2 eats a plurality of holes 14 arranged in the metallization 2 , which are produced by etching. The holes 14 have diameters of approximately twice the metallization thickness, their spacing is approximately the same size. It is not absolutely necessary for the holes to be completely etched through.

A second variant is shown in FIG. 12. There, the metallization 2 is meandered in a designated connection area 13 by etching. The width of the copper layer tape 15 thus produced contributes be about three times that of the copper layer thickness, the spacing between the strips of the meandering Kup ferschichtbandes 15 be about two times the layer thickness. Corners are rounded.

The measure shown in FIGS . 11 and 12 for structuring or weakening the Metallisie tion can be used advantageously when no high currents have to be dissipated and when structuring the metallization is not possible due to space constraints.

The overall proposed process variants are depending on the circumstances individually or in one at a time applicable for the combination deemed appropriate.

Reference symbol list

1 ceramic substrate
2 copper metallization, copper layer
3 crack
4 rounded corners
5 bevelled edge
6 masking
7 thin edge area
8 metallization fingers
9 root
10 soldering area
11 slot
12 sawtooth structure
13 connection area
14 holes
15 copper layer tape

Claims (9)

1. A method for producing a structured copper metallization on a ceramic substrate, wherein a full-area copper layer is first produced by connecting a copper foil to the ceramic substrate by a direct connection method and then the structured copper metallization is produced by masking and etching the copper layer, characterized in that by Masking and a corresponding control of the etching process, the structured metallization ( 2 ) using one of the design options listed below, or any combination thereof is produced:

• a) rounding corners of the copper metallization ( 2 ),
• b) production of an edge region ( 5 ) of the metallization ( 2 ) with a reduced layer thickness,
• c) fraying ( 8 , 12 ) of the edges of the metallization ( 2 ) and
• d) structuring or weakening individual areas of the structured metallization ( 2 ).

2. The method according to claim 1, characterized in that in addition to a rounding of the metallization corners in the region of the corners, a slot ( 11 ) in the metal lamination ( 2 ) is made, from the corners at an angle of 45 ° over a Length of three times the copper layer thickness and with a width of two to three times the copper layer thickness is produced running into the metallization ( 2 ). 3. The method according to claim 1, characterized in that an edge region of the metallization ( 2 ) with ver reduced layer thickness is produced by producing a chamfer with an outwardly decreasing thickness. Is 4. A method according to claim 1, characterized net gekennzeich, that an edge portion of the metallization (2): to reduce thickness by means of a mask (6), Herge which fen in the edge region a narrow Stripes not covering on the copper metallization (2), where a metallization edge with reduced thickness is created by etching and undercutting. 5. The method according to claim 1, characterized in net that the fraying of the metallization by a sawtooth-shaped design of the edge becomes. 6. The method according to claim 1, characterized in net that the fraying of the metallization by a meandering design of the edge becomes. 7. The method according to claim 1, characterized in that an outline of a metallization surface is produced by execution as a meandering copper layer tape ( 15 ). 8. The method according to claim 1, characterized in that an outline or weakening of metallizations ( 2 ) is produced by etching or etching holes ( 14 ). 9. The method according to claim 1, 5 to 8, characterized ge indicates that any outlines or fraying be designed so that the width of copper layers and of distances between the copper layers in the we substantial in the range of about two to three times the Copper layer thickness.