A Comprehensive Guide to Ceramic PCB Manufacturing Processes

1. Introduction to Ceramic PCB Manufacturing Processes

HTCC, DBC, Thick Film Ceramic PCB Manufacturing, LTCC, Thin Film Ceramic PCB Manufacturing, DPC, AMB, etc. are all manufacturing processes for ceramic substrates. Among them, DPC process and DBC process are two commonly used ceramic substrate manufacturing processes. Although they are both methods for making ceramic substrates, there are some important differences between them. Please continue reading and let us introduce them to you in detail.

2. How are ceramic substrates made?

DPC (Direct Plated Copper)

l Principle: DPC process refers to a process of directly plating copper on the surface of ceramics, which can be achieved by electroplating or hot plating. DBC process refers to a process of directly combining copper with ceramics, which is usually made by adding oxygen between copper and ceramics and combining them through chemical metallurgy.

l Process: The ceramic substrate is pre-treated and cleaned, and a copper seed layer is sputtered on the ceramic substrate using a magnetron sputtering process. Then, the circuit pattern is realized through photolithography processes such as exposure, development, etching, and film removal. Finally, the thickness of the copper circuit is increased by electroplating or chemical plating. After removing the photoresist, the metallized circuit is completed.

l Technical key: (1) The bonding strength between the metallized circuit layer and the ceramic substrate is the key to the reliability of the DPC ceramic substrate. Due to the large difference in thermal expansion coefficient between copper and ceramic, in order to reduce the interface stress, a transition layer needs to be added between the copper layer and the ceramic to improve the interface bonding strength. Since the bonding force between the transition layer and the ceramic is mainly based on diffusion adhesion and chemical bonds, metals with high activity and good diffusion such as Ti, Cr and Ni are often selected as transition layers (also as electroplating seed layers).

(2) Electroplating holes is also a key technology for the preparation of DPC ceramic substrates. At present, most of the electroplating holes of DPC substrates use pulsed power supply. Its technical advantages include: easy to fill through holes and reduce plating defects in holes; the surface plating structure is dense and the thickness is uniform; higher current density can be used for electroplating to improve deposition efficiency.

l Advantages: (1) Magnetron sputtering process (below 300℃℃) completely avoids the adverse effects of high temperature on materials or circuit structures, and also reduces the manufacturing process cost.

(2) Thin film and photolithography technology are used to make the metal lines on the substrate more refined (line width size 20~30μm, line alignment accuracy error less than ±196), so DPC substrate is very suitable for electronic device packaging with high alignment accuracy requirements.

(3) The surface roughness is less than 0.5um, which is more suitable for wire bonding, precision cooling chip packaging and other requirements.

l Disadvantages: (1) The thickness of the electroplated copper layer is limited, and the electron microscope waste wave pollution is large

(3) The bonding strength between the metal layer and the ceramic is low, and the reliability of the product is low during application. The process is complicated and the cost is high.

l Application: LiDAR, laser emission segment, radio frequency device, sensor, precision micro cooling chip, aerospace and other fields

DBC (Direct Bonding Copper)

l Principle: DBC is a technology used for surface metallization of ceramic materials, especially for bonded copper processing of alumina (Al2O3) and aluminum nitride (AlN) ceramics.

This technology originated in the 1970s. Its basic principle is to introduce a certain amount of oxygen element on the surface of copper and ceramics, and then in the temperature range of 1000 to 1100 degrees Celsius, copper and oxygen react to form a eutectic phase Cu2O. This eutectic The liquid phase helps improve the wettability of copper on the ceramic surface, thereby achieving a metallurgical bond between the two. During the production process of DBC ceramic substrates, factors such as the oxidation time, oxidation temperature and oxygen partial pressure of the copper plate will have a significant impact on the bonding strength.

DBC ceramic substrates are widely used in power semiconductor modules, solar panel components, and insulated gate bipolar transistors (IGBT) and other packaging devices. However, this method also has some shortcomings. For example, using the eutectic reaction of copper and oxygen at high temperatures requires high precision in equipment and processes, and the bonding strength of DBC has not yet met the needs of some specific application scenarios.

l Process: Add oxygen element between copper and ceramics, and make it through chemical metallurgy. The Cu-0 eutectic liquid is obtained at a temperature of 1065~1083℃, and then the intermediate phase (CuA102 or CuA12 O,) is obtained by the reaction, thus The chemical metallurgical combination of the Cu plate and the ceramic substrate is achieved, and finally pattern preparation is achieved through photolithography technology to form a circuit.

l Technical key: In the preparation process of DBC substrate, it is necessary to strictly control the eutecticity and oxygen content. The oxidation time and gasification temperature are the two most important parameters. After the copper foil is pre-oxidized, the bonding interface can form enough CuxOy Phase wettability of A₂0₂ ceramics and copper foil has high bonding strength. If the copper foil has not been pre-oxidized, the wettability of CuOy will be poor, and a large number of voids and defects will remain at the bonding interface, which will lower the bonding temperature and thermal conductivity. . For the preparation of DBC substrates using AIN ceramics, the ceramic substrate needs to be pre-vaporized to first form an A202 film, and then react with the AIN foil for eutectic reaction.

l Advantages: Since copper foil has good electrical and thermal conductivity, and alumina can effectively control the expansion of the Cu-Al2 O₂-Cu composite, the DBC substrate has a thermal expansion coefficient similar to that of silver oxide, so DBC has good thermal conductivity and insulation Strong performance and high reliability. The process flow is relatively simple and the cost is low

l Disadvantages: (1) The preparation process utilizes the eutectic reaction between Cu and A202 at high temperature (1065°C), which requires high equipment and process control, making the substrate cost relatively high;

(2) Since micropores are easily generated between the Al20 and Cu layers, the thermal shock resistance of the product is reduced. These shortcomings have become a bottleneck in the promotion of DBC substrates.

(3) It can only produce single panels and cannot be used for through-hole conduction applications: it has been widely used in IGBT, LD and CPV packaging, consumer and low-end refrigeration chip markets. Especially because the copper foil is thick (100~600μm), it has obvious advantages in the field of IGBT and LD packaging.

l Application: It has been widely used in IGBT, LD and CPV packaging, consumer and low-end refrigeration chip markets. Especially because the copper foil is thick (100~600μm), it has obvious advantages in the field of IGBT and LD packaging