TECHNICAL FIELD

The present invention relates to a method of producing a ceramic substrate. More particularly, the present invention relates to a method of producing a ceramic substrate by controlling warpage of the ceramic substrate, and to a ceramic substrate produced thereby.

BACKGROUND ART

As well known in the art, a ceramic substrate is formed by integrally attaching a metal foil such as a copper foil to a ceramic base material. The ceramic substrate is manufactured through manufacturing processes such as active metal brazing (AMB), direct bond copper (DBC), and the like and may be classified into a ceramic AMB substrate, a ceramic DBC substrate, and the like depending on the manufacturing process.

While manufacturing of the ceramic DBC substrate involves directly bonding an oxidizable metal to a ceramic base material, manufacturing of the ceramic AMB substrate involves brazing an active metal to a ceramic base material to form a layer and brazing metal to a brazing layer.

In both processes, a metal layer is formed, followed by a photolithography process, and then a pattern layer is formed by etching.

However, in forming metal layers on opposite surfaces of a ceramic base material, the metal layers may differ from each other in area or thickness depending on the arrangement of patterns on the opposite surfaces. When the difference in the area or thickness is greater than a certain ratio, a phenomenon called “warpage” occurs in which a substrate warps toward one of the opposite surfaces under a high temperature environment.

As a result, when the degree of warpage is greater than 0.3%, the substrate is inevitably discarded as a defective product. The incidence rate of which accounts for a relatively large portion of the total production, causing a problem of continuous production loss.

According to empirical data, when the volume ratio between the opposite metal layers reached the range of 75 to 85%, the degree of warpage was greater than 0.3%.

As in an example ofFIG. 1, when the volume ratio between a metal layer2formed on an upper surface of a base material1and a metal layer3formed on a lower surface of the base material is out of an appropriate range, a substrate may warp under a high temperature environment. As shown, a case where the volume of the metal layer3formed on the lower surface is larger is referred to as a negative warpage, and this negative warpage is more likely to occur than a positive warpage, which is the opposite case.

This may be solved by increasing the thickness of the base material. However, this approach is economically limited, and it is common for the base material to maintain a thickness ratio of approximately 1:1 with the metal layers.

The present invention relates to a method of controlling the degree of warpage of a substrate as shown in belowFIG. 1.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.

DISCLOSURE

Technical Problem

Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an objective of the present invention is to provide a method of producing a ceramic substrate by controlling warpage which may occur due to the difference in volume taken up by metal layers on opposite surfaces of a base material, thereby reducing the defect rate of the ceramic substrate, and to provide a ceramic substrate.

Technical Solution

A method of producing a ceramic substrate according to one aspect of the present invention includes: joining a metal layer to each of opposite surfaces of a ceramic base material; forming, on the metal layers, a first electrode layer and a second electrode layer having a larger volume than the first electrode layer; calculating the volumes of the first and second electrode layers; and controlling a thickness of the second electrode layer, thereby controlling warpage which may occur due to a difference between the volumes of the first and second electrode layers.

Furthermore, the controlling the warpage may be performed when a volume ratio of the first electrode layer to the second electrode layer is equal to or greater than 75% to less than 85%.

Furthermore, the controlling the warpage may be performed by controlling the thickness of the second electrode layer such that a volume ratio of the first electrode layer to the second electrode layer after performing the controlling the warpage is 95% (±10%).

The method may further include determining that a failure has occurred when a volume ratio of the first electrode layer to the second electrode layer is less than 75%.

Furthermore, the thickness of the second electrode layer may be controlled by etching.

The present invention also provides a ceramic substrate produced by the above method.

Advantageous Effects

According to a method of producing a ceramic substrate according to the present invention, through control of warpage by eliminating the difference in volume of metal layers formed on opposite surfaces of the ceramic substrate, it is possible to produce a ceramic substrate without warpage under a high temperature environment.

This can result a reduced defect rate of the substrate, thereby improving processability and productivity.

