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What are the common problems of metal PCB?

1. What is the difference between PCB and metal core PCB?

PCB- printed circuit board (PCB) is an electronic circuit used in equipment to provide mechanical support and access to its electronic components.It is made by combining different non-conductive materials, such as fiberglass or plastic, and it is easy to fix the copper circuit.

Metal core PCB – metal core PCB abbreviated as MCPCB, it is made of thermal insulation layer, metal plate and metal copper foil, it has special magnetic conductivity, excellent heat dissipation performance, high mechanical strength and good machining performance.

2. What is the basic material of metal core PCB?

Metal core PCB usually USES aluminum base, iron base (including silicon steel), copper base and CIC as the base materials.

A. aluminum base material

The most common aluminum substrates used to manufacture metal-core PCBS are LF, L4M, and LY12, which require tensile strength of 294N/mm.

The elongation is 5% and the usual thickness is 1mm, 1.6mm, 2mm and 3.2mm.In general, the aluminum layer commonly used in aluminum-based PCB used for communication power supply is 140um thick and copper foil is attached to the top and bottom.

B. copper substrate

Commonly used copper substrates have tensile strengths ranging from 245 to 313.6n/mm2 with an elongation of 12% and usually have five thicknesses of 1mm, 1.6mm, 2mm, 2.36mm and 3.2mm.

C. Iron based substrate

The usual cold-rolled steel used in production is mild steel of 1mm and 2.3mm thickness, or phosphoric iron base steel of 0.5mm, 0.8mm and 1.0mm thickness.

3. Features of metal core PCB

A. heat dissipation

Conventional PCB substrates are generally poor thermal conductors, and the interlayer insulation dissipates heat very slowly.The internal heat of various electronic equipment and electric equipment cannot be eliminated in time, which leads to the failure of high-speed components.Metal core PCB has good heat dissipation.The heat capacity of the metal core is large and the thermal conductivity is high, which can quickly dissipate the heat inside the plate.Heat dissipation is better if the metal core is connected to the housing and the external radiator.Due to the use of metal core PCB in electronic equipment and communication system, the fan in the equipment can be saved, which greatly reduces the size of the equipment and improves the efficiency. It is especially suitable for electronic equipment in closed cases.

B. Thermal expansion

Thermal expansion and cold contraction are the common characteristics of materials, and different materials have different thermal expansion coefficients.PCB is a composite of resin, reinforcement and copper foil.Its coefficient of thermal expansion is anisotropic.In the direction of XY axis, the thermal expansion coefficient CTE of PCB is 13×10-6 ~ 18×10-6 /℃.The thickness direction (z-axis direction) is 80×10-6 to 90×10-6 /°C, the CTE of copper is 16.8×10-6 /°C, and the CTE of flake ceramic body is from 6×10-6 /°C.It can be seen that the metallized hole wall of the PCB is very different from the CTE of the connected insulation substrate on the z-axis.If the generated heat can not be eliminated in time, thermal expansion and contraction can easily lead to metal hole wall coating broken or broken.When the ceramic chip carrier equipment is welded to the PCB, due to the difference between the equipment and the PCB material CTE, the long-term stress will lead to the fatigue fracture of the solder joint.

The thermal expansion rate of metal core PCB is small, and its size varies with temperature more stable than that of insulation PCB.The temperature of aluminum substrate and aluminum sandwich substrate is heated from 30°C to 140-150°C, and the size change is only 2.5% to 3.0%, which can meet the welding reliability requirements of ceramic chip carrier devices.

C. Magnetic shielding

Metal core PCB also has shielding effect, especially CIC core board has good anti-electromagnetic interference performance.It can replace the cooling fin and other components, can effectively reduce the PCB area, but also has the electromagnetic shielding function, can improve the electromagnetic compatibility of the product.Reduce manufacturing costs.

4. USES and characteristics of several common metal core substrates

A. Copper base has good thermal conductivity and is used for heat conduction and electromagnetic interception, but it is of high quality and expensive.

B, iron – anti – electromagnetic interference, the best shielding performance, but poor heat dissipation, cheap price.

C, aluminum – good thermal conductivity, light weight and good electromagnetic shielding.

5. What is a heavy copper PCB?

The thickness of copper on a PCB is usually discussed in terms of “weight” (ounces).For example, a 1-ounce copper layer means 35 microns or 1.4 mil thick.The measurement refers to spreading 1 ounce (28.35 g) of copper evenly over 1 square foot (929cm ^ 2) of PCB area.

Therefore, “heavy copper” refers to the thicker copper conductor layer.Typically, the copper layer of a PCB begins its service life with a solid copper “sheet” (copper foil, which the manufacturer purchases as raw material with some layers of the foil, and other layers that can be pre-laminated onto the fiberglass sheet), and the thickness is uniform throughout the board.

In general, they start very thin — 18um to 35um.After drilling a hole in the PCB, the copper plating process begins to electroplate the inside of the hole.Sometimes a hole is drilled before the etching, sometimes after the etching.It really depends on how many layers and the lamination order.Sometimes the plating is done before the etching, but if the plating is done before the etching, then most of the copper that would have been painstgingly electroplated will be carefully removed again.

Electroplating can be selectively performed – meaning that only specific areas/trace lines are bonded to the PCB – by applying a mask to resist the plating material (copper, nickel, gold or other metals).Heavy copper PCBS may be coated with several layers of copper.

Some of the thicker layers may look like a “wall” on a PCB.20-30 ounces is not a rare thickness.It is noticeably thicker and greatly increases the current carrying capacity as well as the thermal mass of the PCB.

Some plates have a 100% solid metal core.It could be copper.Compared with the thick plate, the copper core plate is very heavy and excellent in heat dissipation.These are called “MCPCBS” or metal-core PCBS, and are different from “heavy copper” PCBS.

6. Why copper is used instead of aluminum in PCB?

The aluminum PCB commonly used in LED products has good heat dissipation, especially the thermal conductivity of manufacturing is higher than 2w/mk, but the multi-layer of this board increases the production cost.

FR4 copper PCB is more flexible and can be designed in multiple layers (such as 10, 12, 20, etc.).

7. What is the difference between aluminum substrate and copper core substrate?

Aluminum substrate circuit printed board made of aluminum core material is called aluminum PCB, due to its strong cooling capacity, this kind of board is usually found in LED lighting products.The front and back have two sides.The white side is welded to the LED pin and the other side is in aluminum form.Usually, apply a heat conducting paste and then make contact with the heat conducting part.

Aluminum substrate is a metal base clad copper laminate with good heat dissipation function.In general, single-sided aluminum PCB consists of three layers, namely the circuit layer (copper foil), the insulation layer and the metal base.It is also used in high-end applications of double-sided design, and its structure is circuit layer, insulation layer, aluminum base, insulation layer and circuit layer.The use of multilayer panels is very rare and may consist of common multilayer panels that combine an insulating layer with an aluminum substrate.

Copper-based circuit board is one of the most expensive metal substrates, and its thermal conductivity is many times higher than that of aluminum or iron substrates.It is suitable for high frequency circuit and high and low temperature variation area as well as precision communication equipment heat dissipation and building decoration industry.

In general, the surface treatment of copper-based circuit boards is impregnated with gold, plated with silver, HAL, OSP, etc.

8. Which one has better thermal conductivity of PCB, ceramic PCB or metal core PCB?

Ceramic PCB is better.Because the ceramic board itself has good insulation, which means it does not need an extra layer of insulation, the thermal conductivity of the ceramic PCB is much better than that of the aluminum PCB(metal-core PCB).

PS: insulation layer is the core technology of all metal plates, its main function is bonding, insulation and heat conduction.In addition, the metal plate insulation layer is the largest insulation layer in the power module structure.

9. How to calculate the copper thickness of PCB?

1. Theoretical calculation formula :Q = I * t & I = j * S

Q: Represents the electric quantity, and on the PCB, it is the thickness of copper plating.

I: Represents the current 2 in electroplating, in A (ampere).

T: Represents the time required for electroplating, in min.

J: Represents the current density, the amount of current per ampere per square foot of area, in the ASF (A/ft2).

S: Represents the plating area in ft2 (square feet).

2. The Practical calculation formula:

Calculation method of copper layer thickness:

Plating thickness (um) = current density (ASF) * Plating time (min) * Plating efficiency * 0.0202

The above calculation formula is for reference only, The electroplating capacity of each company will be different, so The actual electroplating level of your company shall prevail.

10. What is the standard thickness of copper layer on PCB?

Copper weight is defined as the weight (in ounces) of Copper in a square foot area. This parameter specifies the total thickness of the Copper on the layer.

0.5 oz copper (~ 17.5 m thick or 0.7 mils) – Available as part of a “non-standard” construction on inner layers on request. This is also the standard starting copper weight for external layers’printed circuit boards with the choice of copper weight (1 oz)’

1 oz copper (~ 35 m thick or 1.4 mils) – Standard copper thickness of the inner layer for “Standard construction product for the selection of the copper weight for 1 oz and 2 oz”. This is also theStandard copper starting weight on the outer layers for printed circuit boards with the 2 ounce finished copper weight selection.

2 oz copper (70 m thick or 2.8 mils) – standard copper thickness for inner layers when 3 oz copper is selected. This is the standard initial copper thickness on the outer layers for PCBs with the. 2 oz copper (70 m thick or 2.8 mils) – standard copper thickness for inner layers when 3 oz copper is selectedChoice of copper weight (3 oz).


Post time: May-24-2020
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