Understand the technical requirements and production specifications of aluminum substrate PCB in one article
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1. Technical requirements for aluminum substrate The main technical requirements are: Dimensional requirements, including board size and deviation, thickness and deviation, verticality and warpage; appearance, including requirements for cracks, scratches, burrs and delamination, aluminum oxide film, etc.; performance, including peel strength, surface resistivity, minimum breakdown voltage, dielectric constant, flammability and thermal resistance, etc. Special detection methods for aluminum-based copper clad laminates: One is the dielectric constant and dielectric loss factor measurement method, which is a variable Q value series resonance method. The sample and the tuning capacitor are connected in series to a high-frequency circuit to measure the Q value of the series circuit; The second is the thermal resistance measurement method, which is calculated based on the ratio of the temperature difference between different temperature measuring points to the heat conductivity. 2. Aluminum substrate circuit production (1) Machining: Aluminum substrates can be drilled, but after drilling, no burrs are allowed on the edge of the hole, which will affect the withstand voltage test. Milling the shape is very difficult. Punching the shape requires the use of advanced molds, and mold making requires a lot of skills, which is one of the difficulties of aluminum substrates. After punching the shape, the edge is required to be very neat, without any burrs, and not to damage the solder mask on the edge of the board. Usually, a military mold is used, the hole is punched from the circuit, the shape is punched from the aluminum surface, and the force applied when punching the circuit board is shearing up and pulling down, etc. These are all skills. After the shape is punched, the warpage of the board should be less than 0.5%. (2) The aluminum substrate must not be scratched during the entire production process: The aluminum substrate will change color or turn black when touched by hand or exposed to certain chemicals, which is absolutely unacceptable. Some customers also do not accept re-polishing the aluminum substrate, so not scratching or touching the aluminum substrate during the entire process is one of the difficulties in producing aluminum substrates. Some companies use passivation technology, while others apply protective film before and after hot air leveling (spray tin)... There are many tricks, each with its own unique skills. (3) Over-voltage test: Communication power aluminum substrates require 100% high voltage test. Some customers require direct current, some require alternating current, the voltage requirement is 1500V, 1600V, the time is 5 seconds, 10 seconds, and 100% of the printed circuit boards are tested. Dirt on the board surface, burrs on the edges of holes and aluminum substrates, line serrations, and any damage to the insulation layer will cause fire, leakage, and breakdown during the high voltage test. Boards with delamination and blistering during the voltage test will be rejected. 3. Aluminum substrate PCB production specifications 1. Aluminum substrates are often used in power devices with high power density, so the copper foil is relatively thick. If copper foil above 3oz is used, the etching process of thick copper foil requires engineering design line width compensation, otherwise, the line width will be out of tolerance after etching. 2. The aluminum base surface of the aluminum substrate must be protected with a protective film in advance during the PCB processing, otherwise some chemicals will corrode the aluminum base surface, resulting in damage to the appearance. And the protective film is very easy to be scratched and cause gaps, which requires the entire PCB processing process to be inserted. 3. The hardness of the milling cutter used for the fiberglass gong board is relatively small, while the hardness of the milling cutter used for the aluminum substrate is large. During the processing, the milling cutter for producing fiberglass boards rotates fast, while the milling cutter for producing aluminum substrates is at least two-thirds slower. 4. For computer milling edge fiberglass board, just use the machine's own cooling system to dissipate heat, but for processing aluminum substrate, you must add alcohol to the gong head to dissipate heat.
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