JPH01205590A - Circuit board - Google Patents

Abstract

PURPOSE:To prevent chipping or cracks on a periphery of an aluminum nitride substrate surface for applying metallizing past, by forming a gently curved step thereon. CONSTITUTION:A lower stepped section 13 is formed on a periphery of a surface 11a of an AlN substrate 11. The two projecting corner edges of the step 13, that is, a crossing edge section 14 of a rising surface 13b of the step 13 and a surface 11a of the substrate 11, and a crossing stepped section 15 of a bottom 13b of the step 13 and an outer circumference 11b of the substrate 11 are formed in a gently curved surface. Even if impact or load works on the stepped section while handling, stress concentration to the projecting and recessed corner edge sections can be thereby prevented. In this way, chipping of the projecting edge section or cracks on the recessed corner edge section can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a circuit board based on a reramic base, and particularly to a circuit board using an aluminum nitride substrate.

(Prior art) Conventionally, relatively inexpensive alumina (A
j! 203) Those using a substrate are often used. However, in recent years, as the output of semiconductor devices has increased, the amount of heat generated by elements has increased, and the heat dissipation properties of conventional Al2O3 substrates have become insufficient as a heat countermeasure. Therefore, recently, circuit boards using aluminum nitride (Aj!N) substrates, which have excellent heat dissipation properties, have begun to be used.

By the way, in such a circuit board, a metallized layer such as tungsten (W) or molybdenum (Mo) is formed on the surface of the △IN board, and a conductor layer is formed on the surface of this metallized layer by plating with nickel (N: >, etc.). are doing.

A semiconductor element and a lead frame that also serves as an electrode are bonded to this conductor layer.

Formation of the metallized layer on the Δ1N substrate is carried out by applying metallizing paste 1- to the surface of the Δ1N substrate and baking it to harden the metallized portion. In this case, as shown in FIG.
If the peripheral edge surface 1a is cut into a shape perpendicular to the surface portion 1b, the metallization paste 2 applied to the surface will be cut into the peripheral edge portion 1a.
As a result, the withstand voltage may decrease, or cracks may occur in the hanging portion 2a of the metallizing paste 2, resulting in poor metallization.

Therefore, as shown in FIG.
A step portion 3 is formed between the surface portion 1b and the step portion 3, and the hanging portion 2a of the metallizing paste 2 is stopped by the step portion 3, so that the hanging portion 2a of the metallizing paste 2 does not reach the peripheral portion 1a of the AJN substrate 1. is possible.

(Problem to be Solved by the Invention) However, in the circuit board not shown in FIG. 4, the protruding corner edges 3a and 3b of the stepped portion 3 of the AjN board 1 are damaged, and the ζ recessed corner edge 3C is cracked. may occur.

The present invention was made in view of these circumstances, and it not only prevents a drop in withstand voltage due to poor metallization, but also
Prevents damage and cracks from occurring at stepped parts of A, &N boards 1]
2) Provide a circuit board that can be used to cover the 1' target.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a circuit board in which a metallization paste 1 is applied to the surface of an aluminum nitride substrate and then fired to form a metallization layer. The present invention is characterized in that a lower step is formed at the peripheral edge of the surface, and the protruding corner edge and the recessed corner edge of the step are gently curved.

(Function) According to the present invention, the protruding corner edge and the recessed corner edge of the lower step formed on the peripheral edge of the metallizing paste application surface of the aluminum nitride substrate are made into gently curved surfaces. Even if an impact or load is applied to the stepped portion during handling, stress concentration on the protruding corner edges or recessed corner edges of the stepped portion can be prevented.

- The protruding corner edge of C1 was damaged due to impact, and the concave corner edge cracked due to the load - J
- It is possible to prevent damage to the aluminum nitride substrate and maintain the integrity of the aluminum nitride substrate.

Note that the desirable range of the radius of curvature for avoiding stress concentration on the curved surface is 0.01 to 0.5 mm.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 shows the circuit board of this example, with a thermal conductivity of 50
Aluminum nitride (AIN>substrate 11
Tungsten (W> or molybdenum (MO)) on the surface of
A metallized layer 12 is formed, and a semiconductor element such as a silicon chip is mounted on the surface of the metallized layer 12 through a conductive layer (not shown) made of nickel (N i >alloy or other metal).

A lower step 13 is formed at the peripheral edge of the surface 11a of the AfflN 1% board 11, and the bottom surface 13a of the step 13 is approximately parallel to the substrate surface 11a, but the rising surface 13b is parallel to the substrate surface 11a. For example, the slope is inclined at 60° with respect to the slope. Note that the stepped portion 1 from the outer circumferential surface 11b of the A--/-1,-fflN substrate 11 to the center side
The width S of the bottom surface 13a of No. 3 is 0.2 mm, and the step is 0.3 mm.

In this thing, two protruding corner edges of the stepped portion 13 of the AIN board 11, namely the rising surface 13b of the stepped portion 13 and the AIN
The intersecting edge 14 with the surface 11a of the substrate 110, a5, and the intersecting stepped portion 15 between the bottom surface 13b of the stepped portion 13 and the outer peripheral surface 11b of the AJN substrate 11 are each formed into a gently curved surface with a radius of about 0.2 mm. .

In addition, the corner edge of the recess of the stepped portion 13, that is, the bottom surface 13a and the
The concave portion 16 intersecting with the two surfaces 13b is also a gently curved surface with a radius of 0.2 mm.

The metallized layer 12 is formed by applying a metallized paste to the surface 11a of the AfN substrate 11 up to the outer periphery using a printing method to a predetermined thickness, and then baking and hardening it. It is done. In this case, there is a possibility that the metallization paste hangs down from the periphery of the AiN substrate 11, but due to the provision of the stepped portion 13, it stagnates on the vertical angular surface 13b and bottom surface 13a, and the metallization paste hangs down from the outer periphery of the AJ2N substrate 11. It does not hang down to the surface 11. Therefore, the withstand voltage characteristics do not deteriorate.

Furthermore, since the protruding corner edges 14 and 15 of the stepped portion 13 are formed into gently curved surfaces, breakage is unlikely to occur even if an impact force is applied to these portions. Moreover, since the concave corner edge 16 of the stepped portion 13 is also made into a gently curved surface, even if, for example, a load is applied downward in the figure to the bottom surface 13a of the stepped portion 13, stress concentration will not occur and cracks will not occur. Hateful.

Further, such a configuration is extremely effective in maintaining the integrity of the circuit board while achieving economic efficiency and economical efficiency of the circuit board.

That is, if the metallizing paste 1 is applied to a certain area of the surface of the AJN substrate 11 excluding the peripheral edge, the metallizing paste will not sag, so there is no need to provide the stepped portion 13. However, In this case, an extra area larger than the metallized layer will be required for the AJN board 11, which will make the printed circuit board into a doll and a high cost. Perhaps because of the formation, if left as is, chips or cracks may occur in the stepped portion 13, which may impair its integrity.On the other hand, by making the stepped portion 13 a curved surface, chips or cracks can be prevented. , it will be possible to maintain soundness as well as to reduce costs and reduce costs.

Particularly for increasing the capacity of semiconductor circuit boards, there is a great advantage in that the AfN base 11, which has excellent heat dissipation properties, can be used more effectively.

41, as shown in FIG. 2, for an AJN board 11' having substantially the same shape and dimensions as those of the previous embodiment, the protruding corner edges 14' and 15' of the stepped portion 13' and the recessed corner edges 16'
When we made a prototype with a curved surface and compared it with the one in the previous example, we found that the protruding corner edges 14', 15' were damaged or the corner was depressed due to a smaller impact or load than the one in the previous example. It was observed that cracks occurred at the edge 16'.

A3: In the present invention, the dimensions and specific shapes etc. shown in the above embodiments are not necessarily adopted, and various modifications, applications, etc. can be made within the range that can prevent chipping of the stepped portion and generation of cracks. Of course, this is possible.

[Effects of the Invention] As described above, according to the present invention, by forming the stepped portion formed at the peripheral portion of the metallizing paste application surface of the aluminum nitride substrate into a gently curved surface, it is possible to prevent defects and cracks from occurring in that portion. This has the excellent effect of not only preventing a drop in withstand voltage due to poor metallization but also significantly improving soundness.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a partially enlarged cross-sectional view showing an embodiment of a circuit board according to the present invention, FIG. 2 is a partially enlarged cross-sectional view showing a comparative example, and FIG.
This figure and FIG. 4 are partially enlarged sectional views showing conventional examples different from each other. 11...AIN board, 11a...surface, 11b...
・Outer peripheral surface (side surface), 12...Metallized layer, 13...
・Double section, 1/1. ．． 15...Protruding corner edge, 16...
- Concave corner edge. Figure 3 Figure 4

Claims (1)

[Claims] In a circuit board formed by applying a metallization paste to the surface of an aluminum nitride substrate and firing it to form a metallization layer, a lower step is formed at a peripheral portion of the surface for applying the metallization paste of the aluminum nitride substrate, A circuit board characterized in that a protruding corner edge and a recessed corner edge of the stepped portion are formed into gently curved surfaces.