MC PCB
As a metal - core printed circuit board (MCPCB) with copper as the base material, the copper base board has become the core carrier for resolving the "high - power - high - heat - dissipation" contradiction, thanks to its excellent thermal conductivity (thermal conductivity coefficient can reach 10 - 400W/(m·K)), good mechanical strength, and electromagnetic shielding properties
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I. Core Definition and Structural Advantages of Single - sided Copper - based PCB
A single - sided copper - based PCB refers to a metal - based PCB where only the "insulating and thermally conductive layer + circuit copper foil" is compounded on a single surface of the copper base material, and component soldering and signal transmission are achieved only through the top - layer circuit. Its core design logic is "simplifying the structure and focusing on basic needs". Compared with double - sided copper - based PCBs (with circuit layers on both sides), single - sided copper - based PCBs eliminate the etching of the bottom - layer circuit and the coating process of the insulating layer. While retaining the high thermal conductivity of the copper base material, they significantly reduce manufacturing costs and process difficulties. Compared with traditional single - sided FR4 PCBs (non - metal - based), the core advantages of single - sided copper - based PCBs are concentrated in three aspects:
- Leap - forward improvement in heat - dissipation capacity: The thermal conductivity coefficient of the base material of traditional single - sided FR4 PCBs is only 0.3 - 0.6W/(m·K), while that of the copper base material of single - sided copper - based PCBs can reach 10 - 400W/(m·K) (depending on the purity of the copper base material). Even after the loss of the insulating and thermally conductive layer, the overall heat - dissipation efficiency is still 5 - 20 times that of FR4 PCBs. This can effectively prevent performance degradation of medium - and low - power components (such as 1 - 50W LEDs, small power chips) caused by heat accumulation.
- Better mechanical stability: The tensile strength of the copper base material (about 220MPa) is much higher than that of the FR4 base material (about 100MPa). In high - temperature soldering (such as reflow soldering with a peak of 260℃) or slightly vibrating environments, single - sided copper - based PCBs are less likely to have problems such as base - material deformation and circuit breakage. They are suitable for scenarios with basic reliability requirements, such as small home appliances and automotive auxiliary electronics.
- Stronger electromagnetic shielding: The copper base material itself has excellent electromagnetic shielding capabilities (shielding effectiveness ≥ 40dB), which can reduce the impact of external electromagnetic interference on circuit signals and avoid interference from the PCB's own circuits to surrounding components. This is crucial for the application of sensitive components such as RF modules and sensors.
II. Three - layer Core Structure of Single - sided Copper - based PCB
Single - sided copper - based PCBs adopt a three - layer composite structure from top to bottom. The material selection, thickness design, and functional positioning of each layer highly match the requirements of medium - and low - power scenarios. The specific structural details are as follows:
| Structural Layer | Common Materials | Typical Thickness Range | Core Function and Design Considerations |
|---|---|---|---|
| Circuit Layer (Top Layer) | Electrolytic copper foil (purity ≥ 99.8%) | 18μm, 35μm, 70μm | Etched to form circuits for soldering electronic components (such as LED lamp beads, resistors, capacitors). The thickness selection should match the current demand - 18μm copper foil is suitable for small currents ≤ 1A, and 70μm copper foil can carry 3 - 5A currents, meeting the needs of small - power modules. |
| Insulating and Thermally Conductive Layer (Middle Layer) | Epoxy resin + Al₂O₃ filler, modified epoxy resin + MgO filler | 50μm - 150μm | A key layer connecting the circuit layer and the copper base material: ① Achieves electrical insulation (breakdown voltage ≥ 1.5kV/mm to avoid short - circuits between the circuit and the base material); ② Transfers the heat from the circuit layer to the copper base material (thermal conductivity is usually 1 - 4W/(m·K), matching medium - and low - power heat - dissipation requirements). If the thickness is too thick, it will increase the thermal resistance; if too thin, it will reduce the insulation safety. A balance needs to be struck according to the voltage level. |
| Copper Base Material Layer (Bottom Layer) | Red copper (T2/T3, purity ≥ 99.9%), brass (H62) | 0.3mm, 0.5mm, 1.0mm | The "core for heat - bearing and heat - diffusion": Receives the heat conducted from the insulating layer and dissipates it through natural convection on the surface or by attaching a simple heat sink (such as an aluminum heat sink). At the same time, it provides mechanical support for the PCB. A thickness of 0.3 - 0.5mm can balance light - weight and rigidity, suitable for compact - space scenarios (such as LED bulbs, small sensors). |
It should be noted that the insulating and thermally conductive layer of single - sided copper - based PCBs is the key to performance. Since it relies on a single insulating layer for both insulation and heat conduction, more attention needs to be paid to the balance of "insulation - heat conduction - cost" in material selection. For example, single - sided copper - based PCBs used in household LED bulbs mostly use an "epoxy resin + low - content Al₂O₃" insulating layer (thermal conductivity 1 - 2W/(m·K)), which has a low cost and meets the heat - dissipation requirements of 1 - 10W LEDs. However, products used in automotive ambient lights need to select a "modified epoxy resin + medium - content Al₂O₃" insulating layer (thermal conductivity 2 - 4W/(m·K)) to improve temperature resistance (long - term operating temperature ≤ 150℃) and vibration resistance.
III. Core Classification of Single - sided Copper - based PCB
According to the differences in the materials of the insulating and thermally conductive layer, the types of copper base materials, and application scenarios, single - sided copper - based PCBs can be divided into three categories, with significant differences in performance positioning and application ranges for different types:
(1) Classification by Materials of the Insulating and Thermally Conductive Layer
This is the most core classification method, directly determining the heat - dissipation capacity and cost of single - sided copper - based PCBs:
- Single - sided Copper - based PCB with Ordinary Epoxy Resin TypeThe insulating layer uses general - purpose epoxy resin as the matrix and is filled with 10% - 30% Al₂O₃ filler. It is currently the most widely used type in the market (accounting for over 70%).Advantages: Extremely low cost (about 0.5 - 1.5 yuan/cm²), mature process, good resistance to heat and humidity (no attenuation of insulation performance after being placed in an 85℃/85% RH environment for 500 hours).Limitations: Low thermal conductivity (1 - 2W/(m·K)), long - term operating temperature ≤ 120℃.Application Scenarios: Medium - and low - power LED lighting (such as household LED bulbs, LED light strips), small - power adapters (5 - 15W), auxiliary circuits in consumer electronics (such as router power modules).
- Single - sided Copper - based PCB with Modified Epoxy Resin TypeThe insulating layer uses high - temperature - resistant modified epoxy resin (such as modified with phenolic resin or silicone resin) and is filled with 30% - 50% Al₂O₃ or MgO filler, focusing on temperature and heat - dissipation upgrades.Advantages: Thermal conductivity is increased to 2 - 4W/(m·K), long - term operating temperature ≤ 150℃, and stronger chemical corrosion resistance (can withstand weak acid - base environments).Limitations: The cost is 30% - 50% higher than that of the ordinary type.Application Scenarios: Automotive electronics (such as automotive LED ambient lights, dashboard backlights), small modules in industrial control (such as sensor signal - processing boards), outdoor LED signage lights (10 - 30W).
- Single - sided Copper - based PCB with Ceramic - filled TypeThe insulating layer uses epoxy resin as the matrix and is filled with high - performance ceramic fillers such as AlN (aluminum nitride) or SiC (silicon carbide), belonging to the high - end type.Advantages: Thermal conductivity reaches 4 - 8W/(m·K), breakdown voltage ≥ 3kV/mm, high - temperature resistance (long - term operating temperature ≤ 180℃).Limitations: High cost (about 2 - 5 yuan/cm²), and the insulating layer is slightly more brittle.Application Scenarios: High - power LED spotlights (30 - 50W), small - power semiconductor modules (such as MOSFET driver boards), auxiliary circuits in medical equipment (such as the power supply of small laser therapy devices).
(2) Classification by Types of Copper Base Materials
- Single - sided Copper - based PCB with Red Copper Base Material: The purity of red copper is ≥ 99.9%, and the thermal conductivity is about 401W/(m·K). It has the best heat - dissipation performance and is suitable for scenarios with high heat - dissipation requirements (such as 30 - 50W LEDs).
- Single - sided Copper - based PCB with Brass Base Material: Brass contains about 62% copper, and the thermal conductivity is about 109W/(m·K). The cost is 20% - 30% lower than that of red copper, but the heat - dissipation ability is weaker. It is suitable for low - power scenarios (such as 1 - 5W LED indicator lights).
IV. Key Performance Indicators of Single - sided Copper - based PCB
The core indicators for evaluating the quality of single - sided copper - based PCBs revolve around the three major needs of "basic heat - dissipation, electrical safety, and mechanical reliability", with the following specific requirements:
(1) Heat - dissipation Performance Indicators
- Core Indicators: Thermal Resistance and the thermal conductivity of the insulating layer.
- Industry Standards: Thermal resistance should be ≤ 3℃/W (for 10W power scenarios). The thermal conductivity of the insulating layer is divided into 1 - 2W/(m·K) (ordinary type), 2 - 4W/(m·K) (modified type), and 4 - 8W/(m·K) (ceramic - filled type) according to the type.
- Test Methods: Test thermal resistance according to the IPC - TM - 650 2.4.14 standard, and test the thermal conductivity of the insulating layer by the laser flash method.
(2) Electrical Safety Indicators
- Core Indicators: Breakdown voltage, volume resistivity.
- Mandatory Requirements: Breakdown voltage ≥ 1.5kV/mm (ordinary type), ≥ 2kV/mm (modified type) to avoid insulation - layer breakdown and short - circuits in high - voltage scenarios. Volume resistivity ≥ 10¹⁴Ω·cm to ensure no leakage risk in the insulating layer.
- Test Standards: Test breakdown voltage according to the GB/T 1408.1 standard, and test volume resistivity according to the ASTM D257 standard.
(3) Mechanical Reliability Indicators
- Core Indicators: Peel strength, flexural strength.
- Key Requirements: The peel strength between the circuit - layer copper foil and the insulating layer should be ≥ 1.2N/mm (to prevent the copper foil from falling off when soldering components), and the flexural strength of the copper base material should be ≥ 200MPa (red copper), ≥ 300MPa (brass) to ensure that the PCB is not easily deformed during the assembly process.
- Test Standards: Test peel strength according to the IPC - TM - 650 2.4.8 standard, and test flexural strength according to the GB/T 228.1 standard.
V. Manufacturing Process of Single - sided Copper - based PCB
The manufacturing process of single - sided copper - based PCBs is more concise than that of double - sided copper - based PCBs. The core links are concentrated in "insulating - layer coating" and "circuit etching". The typical process steps are as follows:
(1) Pretreatment of Copper Base Material
- Use the "pickling - passivation" process: First, remove the oxide layer on the surface of the copper base material with a 10% - 15% hydrochloric acid solution (processing time of 5 - 10 minutes), and then passivate it with a chromate solution (forming a passivation film with a thickness of 1 - 2μm). This not only improves the bonding force with the insulating layer but also enhances the oxidation resistance of the copper base material.
- Slightly sand - blast the surface of the copper base material (roughness Ra = 0.8 - 1.5μm) to avoid bubbles during the coating of the insulating layer.
(2) Coating and Curing of the Insulating and Thermally Conductive Layer
- Mix epoxy resin, thermal conductive filler (Al₂O₃/AlN), curing agent, and diluent according to the formula, and make a uniform thermal conductive slurry through high - speed stirring (rotation speed of 3000 - 5000rpm).
- Use the doctor - blade coating process (coating speed of 1 - 2m/min) to evenly coat the slurry on the surface of the pretreated copper base material, with the thickness controlled at 50 - 150μm.
- Cure in stages: First, pre - cure in an 80℃ oven for 30 minutes (to make the slurry initially take shape), and then raise the temperature to 150 - 170℃ and cure for 60 - 90 minutes (to ensure that the insulating layer is fully cross - linked and improve heat - conduction and insulation performance).
(3) Preparation of the Circuit Layer
- Copper - foil Lamination: Laminate the electrolytic copper foil (18μm/35μm/70μm) onto the surface of the cured insulating layer through a hot - pressing process (temperature of 120 - 140℃, pressure of 15 - 20kg/cm²).
- Circuit Etching: Coat photoresist on the copper - foil surface → Transfer the circuit pattern to the photoresist through an exposure machine (exposure time of 10 - 20 seconds) → Use a developer to remove the unexposed photoresist → Etch the unprotected copper foil with a ferric chloride solution (concentration of 38% - 42%) (etching temperature of 40 - 50℃) → Remove the photoresist (remove the remaining photoresist) to finally form the required circuit.
(4) Post - treatment and Inspection
- Surface Treatment: Tin - spray (thickness of 5 - 10μm) or gold - plating (thickness of 0.1 - 0.3μm) the circuit pads to improve the oxidation resistance and solderability of the pads.
- Shape Processing: Cut the PCB to the designed size (accuracy of ±0.1mm) through a CNC punching machine or laser cutting.
- Quality Inspection: Conduct thermal - resistance testing, breakdown - voltage testing, and peel - strength testing, and eliminate unqualified products (the pass rate is usually ≥ 95%).
VI. Typical Application Scenarios of Single - sided Copper - based PCB
The applications of single - sided copper - based PCBs always focus on the three major needs of "medium - and low - power, cost - sensitive, and basic heat - dissipation", mainly covering four fields:
(1) Medium - and Low - power LED Lighting Field
This is the most core application scenario of single - sided copper - based PCBs (accounting for over 60%). If the heat generated during the operation of LED chips cannot be dissipated in time, it will accelerate light decay (for example, for a 10W LED, when the temperature is 80℃, the lifespan is reduced from 50,000 hours to 20,000 hours). The heat - dissipation capacity of single - sided copper - based PCBs exactly meets this need.
- Specific Applications: Household LED bulbs (1 - 10W), LED downlights (5 - 20W), LED light strips (10 - 20W per meter), outdoor LED signage (10 - 30W).
- Selection Logic: For ordinary household scenarios, choose the "ordinary epoxy resin type + red copper base material" (low cost), and for outdoor or automotive scenarios, choose the "modified epoxy resin type + red copper base material" (good temperature and weather resistance).
(2) Consumer Electronics Power Field
The power modules (5 - 15W) of small - power adapters, chargers, and other devices, although not high in power, still generate heat accumulation during long - term operation. Traditional FR4 PCBs are prone to problems such as capacitor bulging and chip burnout, which can be effectively solved by single - sided copper - based PCBs.
- Specific Applications: Mobile - phone chargers (5 - 65W, such as the iPhone 20W charger), router power supplies (12 - 24W), power supplies for smart home devices (such as smart - speaker power supplies).
- Selection Features: Mostly use the "ordinary epoxy resin type + brass base material" to control costs while meeting heat - dissipation requirements. The cost of a single PCB can be controlled at 1 - 3 yuan.
(3) Automotive Electronics Auxiliary Field
The auxiliary modules in automotive electronics (such as ambient lights, dashboard backlights, small sensors) have low power (1 - 10W), but have strict requirements for temperature resistance (-40℃ - 125℃) and vibration resistance. The modified - epoxy - resin - type single - sided copper - based PCB becomes an ideal choice.
- Specific Applications: Automotive LED ambient lights (1 - 5W), dashboard LED backlights (3 - 8W), reverse - radar sensor circuits (5 - 10W).
- Compliance Requirements: Need to comply with automotive - electronics industry standards (such as the IATF 16949 quality system), and the insulating layer needs to pass the heat - and - humidity cycle test (-40℃ - 125℃, 1
