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PCB Tech

PCB Tech

Classification of PCB aluminum substrates and thermal conductivity of aluminum substrates in HDI factory
2021-09-08
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Author:Belle

The PCB aluminum substrates of HDI factory have many names, such as aluminum cladding, aluminum PCB, metal clad printed circuit board (MCPCB), thermally conductive PCB, etc. The advantage of PCB aluminum substrate is that the heat dissipation is significantly better than the standard FR-4 structure. The dielectric is usually 5 to 10 times the thermal conductivity of conventional epoxy glass, and the thickness of one-tenth of the heat transfer index is more efficient than the traditional rigid PCB. Let’s understand the types of PCB aluminum substrates below.


PCB aluminum substrate classification


  1. Flexible aluminum substrate

  One of the latest developments in IMS materials is flexible dielectrics. These materials can provide excellent electrical insulation, flexibility and thermal conductivity. When applied to flexible aluminum materials such as 5754 or similar, products can be formed to achieve various shapes and angles, which can eliminate expensive fixing devices, cables and connectors. Although these materials are flexible, they are designed to bend in place and remain in place.


2. Mixed aluminum aluminum substrate


  In the "hybrid" IMS structure, the "sub-components" of non-thermal substances are processed independently, and then AmitronHybridIMSPCBs are bonded to the aluminum substrate with thermal materials. The most common structure is a 2-layer or 4-layer sub-assembly made of traditional FR-4, which can be bonded to an aluminum substrate with a thermoelectric to help dissipate heat, increase rigidity, and act as a shield. Other benefits include:


1. The cost is lower than the construction of all heat-conducting materials.

2. Provide better thermal performance than standard FR-4 products.

3. Expensive radiators and related assembly steps can be eliminated.

4. It can be used in RF applications that require the RF loss characteristics of the PTFE surface layer.


5. Use component windows in aluminum to accommodate through-hole components. This allows connectors and cables to pass the connector through the substrate while welding rounded corners to create a seal without the need for special gaskets or other expensive adapters.


3, multilayer aluminum substrate


According to the editor of HDI, in the high-performance power supply market, multi-layer IMSPCB is made of multi-layer thermally conductive dielectric. These structures have one or more layers of circuits buried in the dielectric, and blind vias are used as thermal vias or signal paths. Although single-layer designs are more expensive and less efficient to transfer heat, they provide a simple and effective cooling solution for more complex designs.


4, through-hole aluminum substrate


  In the most complex structure, a layer of aluminum can form the "core" of a multilayer thermal structure. Before lamination, aluminum is electroplated and filled with dielectric in advance. Thermal materials or sub-components can be laminated to both sides of the aluminum using thermal adhesive materials. Once laminated, the finished assembly resembles a traditional multilayer aluminum substrate by drilling. Plated through holes pass through gaps in the aluminum to maintain electrical insulation. Alternatively, the copper core may allow direct electrical connection as well as insulating vias.

 multilayer aluminum substrate

  The thermal conductivity of the aluminum substrate refers to the heat dissipation performance parameter of the aluminum substrate, which is one of the three major standards to measure the quality of the aluminum substrate (the other two standards are the thermal resistance value and the withstand voltage value). The thermal conductivity of the aluminum substrate can be obtained by testing the test instrument after the sheet is pressed. The current high thermal conductivity is generally ceramic, copper, etc. However, due to cost considerations, most of the aluminum substrates in the market are currently on the market. The thermal conductivity of the aluminum substrate is a parameter that everyone cares about. The higher the thermal conductivity, the better the performance.


Thermal conductivity of PCB aluminum substrate


  Aluminum substrate is a unique metal-based copper-clad aluminum substrate, which has good thermal conductivity, electrical insulation properties and mechanical processing properties. Under normal circumstances, the HDI factory will have the application of aluminum substrates in the LED design and PCB design, and the LED heat dissipation design is based on the simulation and basic design of the fluid dynamics software, which is very important for the production of aluminum substrates. necessary.


  The so-called fluid flow resistance is due to the viscosity of the fluid and the influence of the solid boundary, which causes the fluid to receive a certain resistance during the flow process. This resistance is called the flow resistance, which can be divided into two types: along the way resistance and local resistance; The path resistance is the sudden change of the boundary in the area, such as the sudden expansion or reduction of the section, the elbow, etc., is the flow resistance caused by the sudden change of the fluid flow state.


  Generally, the heat sink used in the LED aluminum substrate is natural heat dissipation. The design process of the heat sink is mainly divided into three steps:


  1. Design the outline drawing of the radiator according to the relevant constraints

  2. Optimize the tooth thickness, tooth shape, tooth spacing and thickness of the aluminum substrate according to the relevant design criteria of the aluminum substrate radiator

  3. Carry out check calculations to ensure the heat dissipation performance of the radiator. "