Raw Materials

The direct raw materials for ceramic copper substrates are mainly copper strips and ceramic substrates, as well as special active metal brazing materials.

Copper strip: Cu-OFE (containing >99.99% copper and <0.0005% oxygen) is now widely used in industry. It is supplied in strips, which should be pressed and cut into copper foils of the same dimensions as the supplied ceramics before use. There are no strict requirements for the storage life of the copper strip, as it is chemically pretreated before bonding.

Reactive metal brazing material: It is a mixed paste with certain adhesive properties. To prevent any change in its properties, it is usually stored at sub-zero temperatures and should be thawed and mixed immediately before use.

Ceramic: The ceramic material used in AMB has high thermal conductivity Si3N4. Si3N4 is supplied in powder form and can be processed into ceramic sheets required for AMB production after a series of mixing, blending, printing and molding.

Screen Printing

Before screen printing, the reactive metal brazing material should be removed from the sub-zero temperature environment and left at room temperature for a period of time to ensure adhesion and printing performance. Before printing, the thawed active metal brazing material should be centrifuged and stirred to remove the air bubbles in the solder and to ensure that the solvent and active agent are fully mixed to prevent the lack of solder during printing. In order to ensure that sufficient solder is left on the surface of the ceramic sheet after printing, the ceramic sheet should be weighed for comparison before and after printing, and if the printing thickness is abnormal, the surface can be scrubbed with alcohol and printed again.

Bonding / Brazing

In AMB preparation, active metal solder is used to bond copper and ceramic substrates. Brazing materials containing elements such as Ti/Ag/Cu react chemically with ceramics to produce a reactive layer that can be wetted by liquid brazing materials, thus enabling metal to be soldered on the surface of the workpiece without metallized ceramics.

Primary etching

Etching: After treatment with the developer, the master card with the pattern is immersed in an acid solution for etching. The copper part of the master card surface not covered by photoresist will be etched away, leaving the part protected by photoresist to form the etched pattern. The brazing material beneath the copper is not etched by the acid solution. The etching depth can be controlled by controlling the concentration of the acid solution and the wire body parameters during the manufacturing process.

Secondary Etching

Etching: The lamination etching process needs to be repeated, but the type of etching solution needs to be adjusted to remove the solder layer.

Electroplating

According to the customer's subsequent applications, different plating treatments can be applied to the surface of the ceramic-copper substrate. The common plating layers used in the industry are silver plating, gold plating, nickel plating, etc.

Laser Cutting

After the chemical plating, the master card is pre-cut along the saw cut street using an industrial laser to prepare for the subsequent manual cutting of the order. As the copper is etched, the laser cutting mainly acts on the sawtooth channel between the single pieces on the ceramic substrate, and the cutting depth should be strictly controlled.

More ceramic substrate process as well as the production can consult Nantong Wispel Semiconductor Co.