Multi-layer Sintered 3D Ceramic Substrate (MSC) Technology Process and Features
Unlike HTCC/LTCC substrates, which are prepared in a single process, Taiwan Sun Rise has prepared MSC substrates using the multiple sintering method. The process flow is shown in Figure 18, where a thick film printed ceramic substrate (TPC) is prepared first, followed by multiple screen printing of the ceramic paste on the flat TPC substrate to form a cavity structure, and then sintered at high temperature to produce the MSC substrate sample shown in Figure 19. Since the ceramic paste sintering temperature is generally around 800°C, the lower TPC substrate line layer must be able to withstand such high temperatures to prevent defects such as delamination or oxidation during the sintering process. As can be seen from the above, the TPC substrate line layer is prepared by high temperature sintering of metal paste (generally 850°C ~ 900°C), which has good high temperature resistance and is suitable for subsequent preparation of ceramic cavities by sintering. The cavity structure and the flat substrate are inorganic ceramic materials with matching coefficients of thermal expansion, so there is no delamination and warpage during the preparation process. The disadvantage is that the lower TPC substrate line layer and the upper cavity structure are screen-printed wiring, and the graphic accuracy is low; at the same time, the thickness (depth) of the prepared MSC substrate cavity is limited due to the screen-printing process. Therefore, MSC three-dimensional substrate is only suitable for small size and low precision requirements of electronic device packaging.
Direct bonding three-dimensional ceramic substrate (DAC) process flow and characteristics.
The above mentioned HTCC, LTCC and MSC substrate line layers are prepared by screen printing with low precision, which is difficult to meet the requirements of high precision and high integration packaging, so the industry proposes to prepare 3D ceramic substrates by molding cavities on high precision DPC ceramic substrates. Since the metal circuit layer of DPC substrate will be oxidized, blistered or even delaminated at high temperature (over 300°C), the preparation of 3D ceramic substrate based on DPC technology must be carried out at low temperature. Taiwan Asperity Corporation (ICP) proposes to use the gluing method to prepare 3D ceramic substrates, and the sample is shown in Figure 20. The metal ring and the DPC ceramic substrate were first processed, and then the metal ring was aligned with the DPC substrate using organic adhesive and then cured by heating, as shown in Figure 21. Because of the good fluidity of the adhesive, the gluing process is simple, low cost and easy to realize mass production, and all the preparation processes are carried out at low temperature without damaging the circuit layer of the DPC substrate. However, due to the poor heat resistance of organic adhesives, the coefficient of thermal expansion between the curing body and metal and ceramic, and non-gas-tight materials, DAC ceramic substrates are mainly used in the packaging of electronic devices with high requirements for line accuracy, but low requirements for heat resistance, gas-tightness, reliability, etc.
In order to solve the above shortcomings, the industry further proposed the use of inorganic adhesive instead of organic adhesive bonding technology solutions, greatly improving the heat resistance and reliability of DAC three-dimensional ceramic substrates. The key is to choose inorganic adhesive, which can be cured at low temperature (below 200°C); the curing body is heat resistant (can withstand 300°C for a long time), good adhesion with metal and ceramic materials (shear strength more than 10 MPa), and match the coefficient of thermal expansion of the metal ring (surrounding dam) and ceramic substrate materials (reduce the interface thermal stress). This technology is used in the packaging substrates of Cree's XRE series, as shown in Figure 22.
Multi-layer plating 3D ceramic substrate (MPC) process flow and characteristics
To exploit the advantages of DPC ceramic substrate technology (high graphic accuracy, vertical interconnection, etc.), Chaohui Wu et al. proposed to prepare a three-dimensional ceramic substrate with a thick copper perimeter dam structure directly on the DPC ceramic substrate by using the multiple/layer plating thickening technique, as shown in Figure 23 (a). The preparation process is similar to that of DPC substrates, except that after the processing of the line layer of the planar DPC substrate, the dam is prepared by multiple lithography, development and pattern plating (thickness generally 500 μm ~ 700 μm), as shown in Fig. 24. It should be noted that due to the limited thickness of the dry film (generally 50 μm ~ 80 μm), repeated lithography, development, and graphic plating are required; at the same time, in order to improve the production efficiency, the current density needs to be increased when plating the thickened barrier, resulting in a rough surface, which needs to be continuously ground to keep the surface flat and smooth.
MPC substrates use the graphic plating process to prepare the line layer, avoiding the problem of rough lines on HTCC/LTCC and TPC substrates, and meeting the requirements of high-precision packaging. The ceramic substrate and metal enclosure are integrated into a sealed cavity with compact structure, no intermediate bonding layer, and high air tightness, and the MPC substrate is an all-inorganic material with good heat resistance, corrosion resistance, and radiation resistance. The shape of the metal barrier structure can be designed arbitrarily, and the positioning steps can be prepared at the top of the barrier to facilitate the placement of glass lenses or cover plates. The disadvantages are: due to the limitation of the dry film thickness, the preparation process requires repeated lithography, development, pattern plating and surface grinding, which is time-consuming (the thickness of 600 μm perimeter dam needs to be plated for more than 10 h) and the production cost is high; in addition, due to the thick copper layer of the plated perimeter dam, the internal stress is high, and the MPC substrate is prone to warpage and deformation, which affects the quality and efficiency of subsequent chip packaging.
Process flow and characteristics of direct molding three-dimensional ceramic substrate (DMC)
In order to improve the production efficiency of 3D ceramic substrates while ensuring the substrate line accuracy and reliability, Chen Mingxiang et al. proposed to prepare 3D ceramic substrates containing no-burning ceramic surround dams, the samples of which are shown in Figure 25. In order to prepare a ceramic dam with high bond strength and high heat resistance, alkali-activated aluminosilicate cement paste (ACP) was used as the dam structure material. The DMC substrate preparation process is shown in Figure 26, where a flat DPC ceramic substrate is prepared and a rubber mold with holes is prepared. After the rubber mold is aligned with the DPC ceramic substrate, the mold cavity is filled with sacrificial mold material; after the sacrificial mold material is cured, the rubber mold is removed and the sacrificial mold is bonded to the DPC ceramic substrate, and the hole structure of the rubber mold is precisely replicated as the aluminosilicate slurry molding mold; then the aluminosilicate slurry is applied to the DPC ceramic substrate and scraped flat, heated and cured, and finally the sacrificial mold material is etched to obtain the aluminosilicate free baking material. Then, the aluminosilicate paste is applied to the DPC ceramic substrate and scraped flat, heated and cured, and finally the sacrificial mold material is etched to obtain a three-dimensional ceramic substrate containing aluminosilicate no-burn ceramic surround dam.
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