Seven preparation technologies for ceramic substrates (3)

Seven preparation technologies for ceramic substrates (3)

2022-05-24 13:35:37 8

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 cured body has good heat resistance (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 (reduce the thermal stress at the interface) of metal ring (surrounding dam) and ceramic substrate materials. 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 perimeter dam, resulting in a rough surface of the plated layer, which requires continuous grinding to keep the surface of the plated layer flat and smooth.


MPC substrate adopts graphic plating process to prepare the line layer, avoiding the problem of rough lines of HTCC/LTCC and TPC substrates, and meeting the requirements of high-precision packaging. The MPC substrate is a fully 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.


Direct Molding Ceramic Substrate (DMC) Process Flow and Characteristics

In order to improve the production efficiency of 3D ceramic substrates and to ensure 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 Fig. 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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The low curing temperature of the aluminosilicate slurry has minimal impact on the line layer of the DPC ceramic substrate and is compatible with the DPC substrate preparation process. The rubber is easy to process, easy to demold, and inexpensive, and can accurately replicate the shape and size of the dam structure (cavity) to ensure the accuracy of dam processing. The experimental results show that the processing error of cavity depth and diameter is less than 30 μm, which indicates that the 3D ceramic substrate prepared by this process is highly accurate, reproducible and suitable for mass production. The aluminosilicate slurry is heated and dehydrated and condensed, and the main product is inorganic polymer, which has good heat resistance, thermal expansion coefficient matching the ceramic substrate and good thermal stability; the cured body has high bonding strength with ceramics and metals, and the prepared 3D ceramic substrate is highly reliable. The thickness of the surrounding dam (cavity height) depends on the thickness of the mold and is theoretically unlimited, which can meet the requirements of different structures and sizes of electronic devices packaging.


Table 3 compares some basic properties of the different 3D ceramic substrate properties described above. Data that duplicate or are similar to Table 2 are not included.

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Ceramic substrate development trend analysis

Ceramic substrate integration: In general, TPC, DBC and AMB ceramic substrates are only suitable for the preparation of single-sided line layer (or double-sided line layer, but the upper and lower layers do not conduct). The HTCC/LTCC substrates are prepared by sintering after stacking (aligning the metal vias) with multiple layers of embryos, thus enabling vertical interconnection within the substrate and improving package integration, but the resistivity of HTCC/LTCC substrates is high. DPC ceramic substrates can be prepared by laser punching (generally 60 μm ~ 120 μm) and electroplated hole-filling technology to produce metal vias, which can realize vertical interconnection between the upper and lower circuit layers of ceramic substrates due to the dense copper pillars filled in the holes and excellent thermal conductivity. On this basis, the three-dimensional ceramic substrate can be prepared by plating and thickening techniques to obtain a three-dimensional ceramic substrate with a dam structure; if multiple DPC substrates are vertically integrated by soldering/bonding techniques, the multilayer ceramic substrate (MLC, Figure 37) can be further obtained to meet the demand for three-dimensional packaging and heterogeneous integration of power devices. The MLC (Figure 37) can be used to meet the demand for 3D packaging and heterogeneous integration of power devices.


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Ceramic substrate gradually to the high power, high integration, high precision, refinement party direction. The requirements for technology are getting higher and higher, and also speak to promote the ceramic substrate continuously upward.


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