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PCB Technology

PCB Technology - Embedded Copper PCB Process and Points to Note

PCB Technology

PCB Technology - Embedded Copper PCB Process and Points to Note

Embedded Copper PCB Process and Points to Note
2023-03-08
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Author:iPCB

Circuit board (PCB) commonly used heat dissipation design generally have a high density set of heat sinks, metal-based circuit boards or circuit board boards welded metal substrates, etc., high density set of heat sinks heat dissipation role is not only limited, but also a waste of drilling space, and metal-based circuit boards or circuit board boards welded metal substrate design there are metal material consumption, bulky, structural design constraints, the cost of high drawbacks.


Embedded copper PCB is in such an environment came into being, the so-called embedded copper board, is embedded in the PCB local or embedded copper, heat electronic components directly mounted on top of the copper block, the use of copper board of high thermal conductivity will be the rapid dissipation of heat out. Embedded copper PCB can not only play a good role in heat dissipation, but also can save space on the board, in recent years has been increasingly used in 5G communication equipment. Circuit board (PCB) commonly used heat dissipation design generally have high density collector heat dissipation holes, metal-based circuit boards or circuit boards of the board surface soldered metal substrate, etc.


High density collector heat dissipation holes heat dissipation effect is not only limited, but also a waste of drilling space, and metal-based circuit boards or circuit boards of the board surface soldering of the metal substrate design of the existence of the consumption of large metal materials, bulky and heavy, limited structural design, the cost of high shortcomings. Embedded copper PCB is in such an environment came into being, the so-called embedded copper block, is embedded in the PCB local or embedded copper, heat electronic components directly mounted on top of the copper block, the use of copper block of high thermal conductivity will be the rapid dissipation of heat out. Embedded copper PCB can not only play a good role in heat dissipation, but also can save the board space, in recent years has been increasingly used in 5G communication equipment.


Embedded Copper PCB production process

Embedded copper block in the PCB, due to the differences in expansion coefficient and thickness between copper block and PCB board, it is easy to have depression, overflow of adhesive and cracks between copper block and resin, which affects the reliability and makes the lamination difficult compared to conventional PCBs. Embedded copper PCB first through the inner layer graphics, etching, milling grooves to produce the inner layer, and then through the formation of a multi-layer circuit board compression, compression of the copper block in the copper block area with the PCB board together with the compression, and then through the immersion of copper, board electricity, back drilling, resin plug holes, secondary immersion of copper, board electricity, etching, solder mask, surface treatment, etc., to get a complete PCB.


Embedded copper PCB specific production process is as follows

1. Inner Layer:Opening → Inner Layer Pattern → Inner Layer Etching → OPE Punching → Milling Inner Slot (Milling Slot for Copper Block Area) → Inner Layer AOI → Brownish → Baking Board → (Turning Pressing)


2. Outer layer:Pressing(copper block and plate are pressed together)→De-flow adhesive→Ceramic grinding plate 1→Slice analysis 1→Drilling target bit hole→Outer layer drilling→Baking plate→Plasma treatment→Beveled edge Causeway platform→Exterior layer copper-immersed 1→Whole plate plating 1→Graphic plating 1(tinned only, no copper plating)→Back drilling→Exterior layer etching 1(etching of copper wires after back drilling, retreated after etching) →Resin plugging →Ceramic grinding plate 2→Ceramic grinding plate 2→Slice analysis 2→Operating layer plasma processing →Ceramic grinding plate 2→Ceramic grinding plate 2→Operating plate 2→The outer layer of ceramic plate is pressed with a copper block. Slicing analysis 2 → outer layer copper-immersed 2 → full-board plating 2 → outer layer graphic → graphic plating 2 → secondary drilling → outer layer etching 2 → impedance test → outer layer AOI → silk-screen soldermask / character element → impedance test → immersion nickel-gold → electrical test → moulding → FQC → FQA → packaging

Embedded copper PCB

Embedded copper PCB


Embedded copper board Note

1. Embedded copper PCB using high-speed plate and buried copper block technology, the compression process should consider both high-speed plate shrinkage, but also consider the impact of buried copper block, compression plate thickness is also the focus of control.


2. The production process, first of all, to ensure that the core board after the opening of the baking board, in order to release the thermal stress within the board to ensure the consistency of shrinkage. The coefficient FA captures the best coefficients of each layer to build up a shrinkage database. The coefficient of expansion of drilled holes and outer layers is limited to ensure the accuracy of the finished product. Adopting the pipeline of "fusion + riveting" before pressing to improve the precision of pre-alignment before pressing.


3. The core plate adopts the method of pre-milling grooves. When pressing, the copper blocks are put into these pre-milled grooves and pressed together with the plate, and the embedded copper blocks are required to be flat to prevent the unevenness of the copper blocks after pressing the plate, and it is necessary to press the copper blocks into the grooves after putting them into the grooves to make sure that the copper blocks are not leaning against the groove walls. The thickness of the pressed plate and the size of the milling groove should be strictly controlled to match with the size of the copper block. Too loose or too tight copper block buried in the groove and the thickness of the copper block relative to the plate will affect the filling of the glue during the pressing process, resulting in insufficient flow of the glue, uneven thickness of the plate, overflowing of the glue to the surface of the copper block or local lack of glue, which affects the appearance, quality and reliability. During the production process, the laminating FA confirms the thickness of the copper block according to the actual test plate thickness of the laminating plate. The milling groove edges are designed with bumps to ensure that the copper blocks are centred. For the lamination stack, a new layer of PP is added to the release film and aluminium sheet, and a new cushion is added to ensure smooth lamination and sufficient glue flow. At the same time, the optimal lamination parameters are determined through DOE testing.


4Due to the influence of high aspect ratio and high-frequency sheet to water surface tension, the hole wall cannot provide uniform and good adhesion to the potion, and the traditional chemical decontamination method, i.e., "KMnO4+NaOH" etching, will easily result in insufficient decontamination. The research adopts plasma to remove adhesive, and the amount of abrasion is controlled at (0.4±0.1) mg/c㎡ with the parameter of plasma. After plating the whole board requires the measurement of glass fibre whitening ≤ 150 μ m, the actual measurement value of 51.87 μ m. Positive concave etching requirements of 5 μ m ~ 80 μ m, the actual measurement value of 10.3 μ m, as shown in Figure 7 to meet the requirements of glass fibre whitening and positive concave etching of the product.


5Back drilling is through the second drilling of the pipeline, has been completed plating PTH (copper plating hole process) holes, not conducive to signal transmission hole copper removal, back drilling after the residual conductor stub (Stub) the shorter, the more favourable to the integrity of the signal transmission. The shorter the stub left after back-drilling, the better for signal transmission integrity. Customers generally require the stub control capability to be ≤0.25mm. The depth of multiple sets of back-drilling varies, and the stub value required by each set of back-drilling is different, making back-drilling more difficult. According to the distribution area of back drilling, set 25 points to measure the board thickness, find out the maximum value, minimum value and extreme value of the board thickness, select the backboard with the biggest extreme value of the board thickness, and set the same depth for back drilling on the same layer. Take the slices of back-drilled holes at the thickest and thinnest places of the board, measure the board thickness and stub length at the sliced position, and calculate the ratio between the sliced thickness extreme, stub extreme and the ratio between the two.

Modelling: Slicing stub control = (actual slicing thickness - minimum measured plate thickness) × coefficient (ratio between stub and slicing plate thickness). Follow up the results of back drilling, back drilling control residual root length needs to meet customer requirements, back drilling control residual thickness to meet the thickness requirements.


6Resin plugging holes, embedded copper block PCB back drilling holes need to be carried out after the resin plugging holes, and high thickness to diameter ratio, a variety of aperture back drilling resin plugging holes in the production of difficult, easy to lead to resin plugging holes in the hole, plugging holes unsaturated and other problems.

Before plugging the holes with resin, the plate should be dried to ensure that there is no moisture in the holes, so as to prevent the subsequent occurrence of hole copper and resin delamination due to moisture in the holes. Stirring and defoaming the resin before use to eliminate the internal air bubbles and reduce the viscosity of the resin to create conditions for plugging holes with a high thickness to diameter ratio of the resin. Use "selective vacuum plugging + double-sided plugging" pipeline for resin plugging, to ensure that the high aspect ratio of small holes in resin plugging holes full, to eliminate air bubbles in the holes. After plugging the holes with resin, the resin is pre-cured by using the segmented baking pipeline.


Specific baking parameters are: 80℃ curing for 20min, 100℃ curing for 20min, 130℃ curing for 20min, 150℃ curing for 30min, to prevent the separation between the resin and the hole copper and the quality problems such as cracks in the resin. At the same time, because the resin is not fully cured, it creates favourable conditions for grinding resin, and the abrasive belt grinding plate avoids deformation of the plate surface and insufficient copper thickness caused by repeated regrinding due to unclean grinding. Follow-up back-drilling resin plug hole production, need to be full of resin in the hole, no air bubbles, holes, hole opening flat, no resin cracks and other quality problems, resin plug hole qualified.


7Impedance control, high-speed circuit signal integrity control and implementation, and transmission line impedance control has a direct relationship, the product impedance line distribution is not uniform, the width of the line is very large, the impedance value of the normal tolerance ± 10% control, part of the impedance value of the ± 8% control. During the manufacturing process, the impedance FA inversely deduces the effective Dk value of the product according to the actual measured impedance. Use dynamic compensation, independent line and dense line difference compensation, reduce the difference in line width. 7, impedance control, high-speed circuit signal integrity control and implementation, and the transmission line impedance control is directly related to the product impedance line distribution is not uniform, the line width of the wide difference, the impedance value of the normal tolerance of ± 10% control, part of the value of the impedance control by ± 8%. During the manufacturing process, the impedance FA inversely deduces the effective Dk value of the product according to the actual measured impedance. Dynamic compensation is used to compensate for the difference between independent lines and dense lines to reduce the difference in line width.

Embedded Copper PCB Stacks

Embedded Copper PCB Stacks

Electronic products in the working period of the electrical energy consumed, in addition to the useful work, most of them will be converted into heat, these heat will make the electronic products within the temperature rises rapidly, if not as soon as the heat dissipation, may lead to some electronic components because of overheating failure, which in turn affects the reliability of electronic products. With the development of electronic products in the direction of light, thin, short and small, and the application and popularity of high-power electronic components, the effective heat dissipation area of electronic products is getting smaller and smaller, and the demand for heat dissipation is getting bigger and bigger, and how to find the best method of heat dissipation and structural design of the antiques has become a great challenge for the electronic design nowadays. 


With the development of new generation information technology, energy saving and new energy vehicles, power equipment, aviation and aerospace fields, the solution of heat dissipation problem is imminent. Embedded copper PCB has high thermal conductivity and high heat dissipation, which can effectively solve the heat dissipation problem of high-power electronic components in special applications. Embedded copper PCB can not only play a good role in heat dissipation, but also can save the board space of the circuit board, has a broad application prospects. 


Electronic products in the working period of the electrical energy consumed, in addition to the useful work, most of which will be converted into heat, this heat will make the electronic products within the temperature rises rapidly, if not as soon as the heat dissipated, may lead to some electronic parts because of overheating failure, which in turn affects the reliability of electronic products. With the development of electronic products in the direction of light, thin, short and small, and the application and popularity of high-power electronic components, the effective heat dissipation area of electronic products is getting smaller and smaller, and the demand for heat dissipation is getting bigger and bigger, and how to find the best method of heat dissipation and structural design of the antiques has become a great challenge for the electronic design nowadays. 


With the development of new generation information technology, energy saving and new energy vehicles, power equipment, aviation and aerospace fields, the solution of heat dissipation problem is imminent. Embedded copper PCB has high thermal conductivity and high heat dissipation, which can effectively solve the heat dissipation problem of high-power electronic components in special applications. Embedded copper PCB can not only play a good role in heat dissipation, but also can save the board space of the circuit board, has a wide range of application prospects.