PCB Technical - Discuss the principle and difference between aluminum substrate and fiberglass board

First,What is fiberglass PCB board

The alias of glass fiber board: glass fiber heat insulation board, glass fiber board (FR-4), glass fiber composite board, which is composed of glass fiber material and high heat resistance composite material, and does not contain asbestos harmful to the human body. It has high mechanical and dielectric properties, good heat resistance and moisture resistance, and good processability. Used in plastic molds, injection molds, machinery manufacturing, molding machines, drilling machines, injection molding machines, motors, PCB.ICT fixtures, and table polishing pads.

1. Advantages of fiberglass board

(1) It has high mechanical properties and electrical resistance, as well as good heat and moisture resistance, and good processability. Generally used in plastic molds and machinery manufacturing.

(2) Injection mold molding usually requires: high temperature material and low temperature mold. The heat insulation method must be adopted under the same machine condition. Keep the injection mold at a low temperature while not making the injection molding machine temperature too high. This requirement can be met by installing an insulation board between the injection mold and the injection machine. Shorten the production cycle, increase productivity, reduce energy consumption, and improve the quality of finished products. The continuous production process ensures stable product quality, prevents overheating of the machine, no electrical failure, and no oil leakage in the hydraulic system.

2. The purpose of fiberglass board

(1) Construction industry: It can be used for cooling towers, building structures, indoor equipment and decorative parts, glass fiber reinforced plastic panels, decorative panels, and solar energy utilization devices, etc.

(2) Chemical and chemical industry: it can be used for corrosion-resistant pipelines, corrosion-resistant pumps and their accessories, grilles, ventilation facilities, and wastewater and sewage treatment equipment, etc.

(3) Automobile and railway transportation industry: It can be used as automobile shell and other parts, as well as the outer shell, door, inner panel and instrument panel of large passenger cars; in the highway construction part, there are road signs, isolation piers and highways. Guardrail and so on.

(4) Glass fiber board performance, glass fiber board, generally can be used for the soft package base layer, and then covered with cloth, leather, etc., can be made into beautiful wall and ceiling decorations.

(5) It has the advantages of sound absorption, sound insulation, heat insulation, environmental protection, and flame retardant. Good insulation characteristics make it already used in the shell of radar, and it is also a good anti-corrosion material. Now it has been widely used in the chemical industry. Fiberglass board has the advantage of strong plasticity.

Second, what is aluminum substrate

The aluminum substrate is a metal-based copper clad laminate with good heat dissipation function. Generally, a single panel is composed of a three-layer structure, which is a circuit layer (copper foil), an insulating layer and a metal base layer. For high-end use, it is also designed as a double-sided board, and the structure is circuit layer, insulating layer, aluminum base, insulating layer, and circuit layer. Very few applications are multi-layer boards, which can be formed by bonding ordinary multi-layer boards with insulating layers and aluminum bases.

1.Advantages of aluminum substrate

(1) The heat dissipation is significantly better than the standard FR-4 structure.

(2) The thermal conductivity of the dielectric used is usually 5 to 10 times that of conventional epoxy glass, and the thickness is only one-tenth.

(3) The heat transfer index is more efficient than traditional rigid PCB.

(4) It is possible to use a lower copper weight than shown in the IPC recommendation chart.

2. The use of aluminum substrate

(1) Audio equipment: input and output amplifiers, balanced amplifiers, audio amplifiers, preamplifiers, power amplifiers, etc.

(2) Power supply equipment: switching regulators, DC/AC converters, SW regulators, etc.

(3) Communication electronic equipment: high-frequency amplifiers, filter appliances, and transmission circuits.

(4) Office automation equipment: motor drives, etc.

(5) Automobiles: electronic regulators, igniters, power controllers, etc.

(6) Computer: CPU board, floppy disk drive, power supply unit, etc.

(7) Power modules: inverters, solid state relays, rectifier bridges, etc.

Aluminum substrates have a wide range of uses. Generally, there are aluminum substrates in audio equipment, power supply equipment, communication electronic equipment, office automation equipment, automobiles, computers, and power modules.

3. Design of aluminum substrate

The main technical requirements are:

Dimension requirements, including board size and deviation, thickness and deviation, perpendicularity and warpage; appearance, including cracks, scratches, burrs and delamination, aluminum oxide film, etc.; performance aspects, including peel strength, surface resistivity, Minimum breakdown voltage, dielectric constant, combustibility and thermal resistance requirements.
Special testing methods for aluminum-based copper clad laminates:
The first is the measurement method of dielectric constant and dielectric loss factor, which is the principle of variable Q series resonance method, which connects the sample and the tuning capacitor to a high-frequency circuit in series 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 measurement points to the amount of heat conduction.

4. Aluminum substrate circuit production
(1) Mechanical processing: Drilling of aluminum substrate is possible, but no burrs are allowed on the edge of the hole after drilling, which will affect the withstand voltage test. Milling the shape is very difficult. The punching shape requires the use of advanced molds, and the mold making is very skillful, which is one of the difficulties of the aluminum substrate. After the contour is punched, the edges are required to be very neat, without any burrs, and not to damage the solder mask on the edge of the board. Normally, using a military maneuver, the hole is punched from the circuit, the shape is punched from the aluminum surface, and the circuit board is punched with upward shear and downward force. These are all techniques. After punching the shape, the warpage of the board should be less than 0.5%.
(2) The whole production process is not allowed to rub the aluminum base surface: the aluminum base surface will be discolored and blackened when touched by hand or through certain chemicals. This is absolutely unacceptable. Re-polishing the aluminum base surface may be used by customers. It is not acceptable, so the whole process does not scratch or touch the aluminum base surface is one of the difficulties in the production of aluminum substrates. Some companies use passivation technology, and some put a protective film before and after the hot air leveling (spraying tin)... There are many tricks.
(3) High voltage test: 100% high voltage test is required for the aluminum substrate of communication power supply. Some customers require direct current, some require alternating current, and the voltage requires 1500V, 1600V, the time is 5 seconds, 10 seconds, and 100% printed board is tested. Dirt, holes, burrs on the edge of the aluminum base, line sawtooth, and scratches on any point of the insulation layer on the board will cause fire, leakage, and breakdown in the high voltage test. The pressure test board was rejected due to delamination and blistering.

5. Specification for aluminum substrate PCB production
(1) Aluminum substrates are often used in power devices, and the power density is high, so the copper foil is relatively thick. If copper foil of more than 3oz is used, the etching process of thick copper foil needs engineering design line width compensation, otherwise, the line width after etching will be out of tolerance.
(2) The aluminum base surface of the aluminum substrate must be protected with a protective film in advance during PCB processing, otherwise, some chemicals will attack the aluminum base surface and cause damage to the appearance. In addition, the protective film is easily scratched, causing gaps, which requires that the entire PCB processing process must be inserted into the rack.
(3) The hardness of the milling cutter used for glass fiberboard gongs is relatively small, while the hardness of the milling cutter used for aluminum substrates is high. During the processing, the speed of the milling cutter for the production of fiberglass board is fast, while the production of aluminum substrate is at least two-thirds slower.
(4) The computer milled fiberglass board can only use the heat dissipation system of the machine itself to dissipate heat, but the processing of aluminum substrates must additionally add alcohol to the gong to dissipate heat.

Three, the three major differences between glass fiber board and aluminum substrate
1. In terms of price
Compared with the price of fiberglass board and aluminum substrate, the price of fiberglass board is obviously much cheaper.
2. Process
According to the different materials and production processes, the fiberglass board can be divided into three types: double-sided copper foil fiberglass board, perforated copper foil fiberglass board and single-sided copper foil fiberglass board. Of course, fiberglass boards made of different materials The price will also be different.
3. Performance
Because the aluminum substrate has good thermal conductivity, the heat dissipation performance of the aluminum substrate is much better than that of the glass fiber board.