The performance, quality, processability in manufacturing, manufacturing level, manufacturing cost, and long-term reliability and stability of PCB aluminum substrates largely depend on aluminum-based copper-clad laminates. Aluminum-based circuit boards have excellent electrical efficiency, heat dissipation capabilities, electromagnetic shielding, high dielectric strength and bending resistance. As a metal core PCB, whether it is a single-layer, double-layer or multi-layer aluminum-based circuit board, they have many similarities with the FR4 circuit board in manufacturing technology, such as etching thick copper foil, aluminum surface etching protection, aluminum plate Manufacturing and solder mask printing, etc. However, as an advanced PCB, aluminum-based circuit boards still have special aspects of the manufacturing process that require strict and effective management and control. So, what are the precautions and manufacturing difficulties in the production of aluminum-based circuit boards?
Aluminum plate
Mechanical processing: Drilling is allowed on the aluminum substrate, but no burrs are allowed on the edge of the hole after drilling, which will affect the pressure test. Milling shapes is very difficult. To punch the shape, you need to use advanced molds. The mold making is very skillful, which is one of the difficulties for aluminum substrates. After the shape is punched, the edges must be very neat, without any burrs, and without damaging the solder mask on the edge of the board. Usually, a manipulator mold is used, the holes are punched from the circuit, the shape is punched from the aluminum surface, and the force when punching the circuit board is to cut up and pull down, etc. are all techniques. After punching the shape, the board warpage should be less than 0.5%.
The aluminum base surface is not allowed to be scratched during the entire production process: the aluminum base surface will cause surface discoloration and blackening if touched by hands or treated with certain chemicals. This is absolutely unacceptable. Some customers will not accept re-polishing the aluminum base surface. , so one of the difficulties in producing aluminum-based circuit boards is that the entire process is not bruised and the aluminum base surface is not touched. Some companies use the passivation process, and some apply protective films before and after hot air leveling (spraying tin). There are many tricks. The eight immortals cross the sea, each showing their magical powers.
Over-voltage test: The aluminum substrate of the communication power supply requires 100% high-voltage test. Some customers require DC power, and some require AC power. The voltage requirement is 1500V, 1600V, and the time is 5 seconds or 10 seconds. 100% printed board is tested. Dirt, holes on the board, burrs on the edges of the aluminum base, jagged lines, and any scratches on the insulation layer will cause fire, leakage, and breakdown during the high-voltage test. The pressure test boards were found to be delaminated and blistered, so they were all rejected.
Thick copper foil etching
Aluminum-based circuit boards are usually used in power devices with high power density, and the copper foil is relatively thick. Trace width compensation is required for etching copper foil when the foil thickness is 3oz or greater. Otherwise, the trace width after etching will be outside the tolerance range. Therefore, in order to ensure the best trace width/spacing and impedance control that can meet the design requirements, the work that must be completed in advance is that trace width compensation should be appropriately designed; the influence of trace manufacturing on trace width/spacing should be eliminated; etching Factors and reagent parameters should be strictly controlled.
Solder mask printing
Solder mask printing is considered a manufacturing difficulty in aluminum-based circuit board manufacturing due to the thick copper foil. If the trace copper thickness after image etching is too large, there will be a large difference between the trace surface and the substrate, and the solder mask will become difficult. In order to ensure smooth solder mask printing, the solder mask oil should be absorbed with high quality and solder mask printing should be used twice. If necessary, the manufacturing method can be used to first fill the resin and then print the solder mask.
Machine made
The mechanical manufacturing of aluminum-based circuit boards includes mechanical drilling, milling and forming as well as V-cutting. Burrs are often left in the internal vias, which will reduce the power intensity. Therefore, in order to ensure high-quality mechanical manufacturing and small batch production, electric milling cutters and professional milling cutters should be selected. During the molding process, attention should be paid to control technology and patterns, and drilling parameters should be appropriately adjusted on thick copper-aluminum-based circuit boards. , to prevent burrs.