Aluminum substrate laser cutting
Aluminum substrate is a type of metal-based copper-clad board with good heat dissipation function.
Generally, a single-sided board is composed of three layers: circuit layer (copper foil), insulation layer, and metal base layer. For high-end use, there are also designs for double-sided boards, with the structure consisting of circuit layer, insulation layer, aluminum base, insulation layer, and circuit layer. A few applications use multilayer boards, which can be made by laminating ordinary multilayer boards with insulation layers and aluminum bases.
LED aluminum substrate is simply a PCB, which means printed circuit board. The difference is that the material of the circuit board is aluminum alloy. In the past, the material for general circuit boards was fiberglass, but because LEDs generate a lot of heat, circuit boards used in LED lamps are generally made of aluminum substrate, which conducts heat quickly.
Compared with traditional FR-4 and fiberglass boards used in other devices or appliances, aluminum substrate can reduce thermal resistance to the lowest, making it excellent in thermal conductivity. Compared with thick film ceramic circuits, its mechanical performance is also excellent.
Aluminum substrate also has the following unique advantages:
- Complies with RoHS requirements
- More suitable for SMT (Surface Mount Technology) process
- Effectively deals with thermal diffusion in circuit design, reducing module operating temperature, extending service life, and improving power reliability
- Reduces the assembly of heat sinks and other hardware (including thermal interface materials), shrinking product size and reducing hardware and assembly costs
- Optimizes the combination of power circuits and control circuits
- Replaces fragile ceramic substrates, obtaining better mechanical durability.
Application of Aluminum Substrate
The aluminum substrate has been increasingly applied in various fields such as hybrid integrated circuits, automobiles, motorcycles, office automation, high-power electrical equipment, power supply equipment, LED lighting, etc. due to its excellent heat dissipation performance, mechanical processing performance, electromagnetic shielding performance, and size stability performance. The demand for it increases every year, and its development prospects are very broad.
Introduction to Traditional Cutting of Aluminum Substrates
The traditional processing methods for aluminum substrates are divided into three categories:
- Typically, CNC drilling/lathing machines are used, which require consumables such as drills, lathes, cushions, and alcohol. The cutting cost is high, the accuracy of the sheet metal forming is low, and the machining groove gap is large (conventional 1.6mm; 2mm lathe groove width), which easily causes substrate deformation.
- Traditional methods such as die stamping forming are used.
- CNC V-CUT cutting method is used, which requires the groove lines to be smooth and burr-free after processing, and the finished products must be evenly without any sharp edges. The board surface must not be scratched, while ensuring the cutting processing of deformed plates and avoiding secondary deformation. The complex process leads to low processing efficiency and low yield. Currently, most PCB companies cut aluminum substrates using lathes to process an entire aluminum substrate. There are still a few burrs on the edge of the finished product on the back of the aluminum plate, which must be manually scraped off, greatly increasing the workload. The increase of the scrap rate due to the board surface scratch, and the large loss of the cutting tools also result in relatively low processing efficiency.
For the CNC forming of assembled aluminum substrates, a 2.0 specialized aluminum substrate milling cutter is used with a feed rate controlled at 0.15m/min and a rotation speed controlled at 30000rpm. It is important to ensure that there are no burrs or warping of the aluminum frame during the process.
Traditional lapping machine process:
- Produces significant burrs and rough edges, requiring manual deburring.
- The tooling and consumables are expensive, and the precision is not high, requiring time-consuming installation and removal of the board using locating pins.
- Shims and alcohol, among other consumables, are needed.
- The production efficiency of the substrate is low.
Advantages and Selection of Laser Cutting Aluminum Substrates
Advantages of laser processing: Laser processing is a non-contact method, without tooling costs, which saves costs and reduces scratches and wear on the material surface. The processing speed is fast, and the precision is high, with small cutting seams and a tolerance range of up to ±0.02mm. The cutting surface is smooth and can be formed in one step, without the need for repeated processing. The operation is simple and does not require a skilled technician. The processing graphics can be edited arbitrarily and CAD drawings can be imported.
Laser processing mainly uses CW lasers and QCW lasers. CW lasers refer to lasers with continuous output without interruption, and the output power is in a constant state. QCW lasers work by operating at intervals, compressing the laser energy to a narrow time frame, resulting in a higher peak power.
Comparison of CW and QCW in laser cutting of aluminum substrates: Continuous laser processing has a fast cutting speed and small kerf, which is widely used in the cutting of aluminum substrates.
However, the output mode of the continuous laser is continuous wave, and when processing parts with high density for a long time, the heat dissipation is relatively slow, which leads to an increase in thermal influence on the cutting surface, affecting the conductivity of the material. In some aluminum substrates with particularly high quality requirements, continuous lasers cannot meet production requirements.
The output mode of pulse lasers is intermittent, and the heat influence generated on the material during processing is relatively small compared to continuous lasers.
However, continuous lasers are much cheaper than pulse lasers. If the product requires high quality and a large processing volume, pulse lasers can be used, while continuous lasers can be used if the processing requirements are not particularly high.
Shortcomings of Laser Cutting Aluminum Substrates
Laser processing belongs to thermal processing, which will inevitably produce thermal effects on the sheet. The cutting principles of CW and QCW lasers are both based on the laser beam emitted by the laser and then irradiated onto the focusing mirror through the optical fiber tube to form refraction.
Finally, the refracted laser beam is transmitted to the cutting head through the cutting nozzle, emitting an extremely small beam of light spot onto the sheet, causing the irradiated material to quickly melt, vaporize, ablate or reach the ignition point.
Meanwhile, the molten material is blown away by the high-speed airflow coaxial with the beam, and finally, the workpiece is cut by the movement of the cutting head. During this process, heat is inevitably formed at the cutting seam, thus forming different degrees of thermal impact width.
When laser processing aluminum substrate, black residue will be left on the cutting section. The surface layer of the aluminum substrate is generally coated with a layer of paint (usually white oil or black oil), and laser cutting requires both high heat and high air pressure to be carried out at the same time.
Therefore, if cutting is performed directly from the front side, the painted surface will directly contact the high-pressure air and high temperature, causing the paint to collapse and scatter.
Therefore, we can only cut from the backside of the sheet during processing. Although cutting from the backside will not damage the paint layer and can achieve the cutting purpose, the high heat generated during cutting will cause the paint surface to ignite instantly when it contacts the paint. The residue of the burned paint will then stay on the cutting section and form a layer of black substance. The thickness of the black substance formed on the cutting section after burning varies with different models and thicknesses of paint.
Laser processing: black substance generated in the thermal processing zone on the back of the heat-affected area formed by laser on the sheet.
By comparing the cutting effect diagrams after two-dimensional amplification of CW and QCW laser cutting, we found that the thermal impact width generated by QCW laser cutting is smaller than that of CW laser cutting, and the cutting surface is smoother. Therefore, high-quality aluminum substrates can be cut using QCW laser cutters.
Solutions to the shortcomings of laser processing aluminum substrates
Solution to the Thermal Effect Generated by Laser Processing on Aluminum Substrate:
The width of the thermal effect generated by laser processing is mainly related to the diameter of the light spot (usually between 0.1mm-0.15mm in diameter), cutting speed, type of paint on the substrate, and thickness of the substrate.
Through continuous sampling testing and long-term after-sales maintenance, it has been found that the width of the thermal effect can be controlled within a certain range by using the open-ink closed-line method.
That is, the shape of the part to be cut is first engraved with a width of 0.1mm-0.15mm on the front of the substrate using a marking machine or micro-carving machine, forming an ink line of the shape to be cut on the front of the substrate.
Then, the cutting can be performed from the reverse side by locating it with CCD vision to control the heat generated by the light spot during cutting within the width of the ink line, thus controlling the width of the thermal effect within 0.15mm.
In the process of making the circuit board engineering drawing, the appropriate ink window width should be reserved for the screen printing process to ensure the stability of the quality of the cutting process.
Solution to the Black Residue Left on the Cutting Section of the Laser-Processed Aluminum Substrate:
Through continuous process testing, we have found that the substance covering the cutting section is the paint that has burned during high-heat laser processing, and it adheres to the cutting section under the action of high-pressure gas. It can be easily removed by wiping with alcohol, but the efficiency of individual wiping is low, and a large amount of manpower is needed, so it is not feasible.
Through continuous testing and experiments, we have found that high-power multi-head ultrasonic cleaning with detergent and water can be used to clean the well-cut substrate. The substrate cleaned by ultrasonic waves is not only clean and smooth but also does not affect the electrical conductivity and other qualities of the substrate.
Moreover, it can be cleaned in large quantities at the same time, with high cleaning efficiency, without affecting normal production.
After multiple communications and discussions with customers, it has been unanimously agreed that this solution is feasible.
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