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More easily dissipated PCB - Aluminum Board

Nov 07, 2018

What is an aluminum board


A PCB is a printedcircuit board, or printedcircuit board.

Aluminum Board is a kind of PCB:


Aluminum board is a kind of metal base copper plate with good heat dissipation function. Generally, single panel is composed of three layers, namely circuit layer (copper foil), insulation layer and metal base layer.

For high-end use are also designed as double panel, and the structure is circuit layer, insulation layer, aluminum base, insulation layer, circuit layer.

Very few applications are multi-layered, which can be made by ordinary multi-layered board with insulating layer and aluminum base.

QQ图片20181107120136



One - sided aluminum substrate: it is only one layer of conductive graphics layer with insulating material aluminum (substrate).



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Double-sided aluminum substrate: there are two conductive graphic layers which are superimposed on the insulating material and aluminum substrate.





Multilayer printed aluminium base circuit board: printed circuit board made of three or more layers of conductive graphics and alternating lamination of insulating material and aluminum base plate.

 







Divided by surface treatment:


Gold plate




Electric gold plate




Tin plate

Molten tin plate

Heavy tin plate

Heavy silver plate

Electric silver plate

Heavy palladium plate


Working principle of aluminum substrate


The surface of the power device is mounted on the circuit layer, and the heat generated during the device operation is quickly transferred to the metal base through the insulation layer, and then the heat is transferred from the metal base to realize the heat dissipation of the device (see figure 2).


Compared with the traditional FR-4 ratio, aluminum substrate can reduce the thermal resistance to the minimum, so that aluminum substrate has excellent thermal conductivity.

Compared with the thick - film ceramic circuit, its mechanical properties are excellent.


In addition, aluminum substrate has the following unique advantages:


Comply with RoHs requirements;


More suitable for SMT process;


The thermal diffusion is treated effectively in the circuit design scheme, so as to reduce the operating temperature of the module, extend the service life, and improve the power density and reliability.


Reduce the assembly of radiators and other hardware (including thermal interface materials), reduce product volume, and reduce hardware and assembly costs;

Optimize the combination of power circuit and control circuit;


Replace fragile ceramic substrate for better mechanical durability.



The composition of aluminum substrate


1. The circuit layer


The circuit layer (usually electrolytic copper foil) is etched to form printed circuit, which is used to realize the device assembly and connection.

Using the same thickness, the same line width, the aluminum substrate is capable of carrying higher currents than conventional fr-4.


2. The insulation layer


Insulating layer is the most core technology of aluminum substrate, which mainly functions as adhesion, insulation and heat conduction.

The insulating layer of aluminum substrate is the largest thermal barrier in power module structure.

The better the insulation layer's thermal conductivity is, the more conducive it is to the heat diffusion generated during the device's operation, and the more favorable it is to reduce the device's operating temperature, so as to improve the power load of the module, reduce the volume, prolong the life and improve the power output.


3. Metal base


The type of metal used in insulating metal substrate depends on the comprehensive consideration of the thermal expansion coefficient, thermal conductivity, strength, hardness, weight, surface condition and cost of the metal substrate.


QQ图片20181107120345

Properties of aluminum substrate


I. heat dissipation


At present, many double panel, multilayer board density is high, power is big, quantity of heat sends out is difficult.

Conventional PCB substrates, such as FR4 and CEM3, are poor conductors of heat.

The aluminum substrate can solve the heat dissipation problem, which is caused by the local heating of electronic devices.


2. Thermal expansion


Heat expansion and contraction are the common nature of matter.

Aluminum base PCB can solve the heat dissipation problem effectively, so that the problem of heat expansion and cold shrinkage of components and components on the PCB can be alleviated, and the durability and reliability of the whole machine and electronic equipment can be improved.

Especially solve the problem of hot expansion and cold shrinkage of SMT (surface mount technology).


Dimensional stability


Aluminum - based PCB is obviously much more stable in size than insulating PCB.

Aluminum base PCB, aluminum sandwich board, from 30 ℃ heating to 140 ~ 150 ℃, size of 2.5 ~ 3.0%.


4. Other reasons


Aluminum substrate board, with shielding function;

Replacing brittle ceramic substrates;

Safe use of surface mounting technology;

Reducing the real effective area of the PCB;

It replaces radiators and other components to improve heat resistance and physical properties.

Reduce production costs and labor.


V. technological process of aluminum substrate manufacturing







A) cutting


1. Material opening process


Incoming, open, baking


Material: the raw material made of thermal conductive material or semi-solidified sheet and pressed on aluminum foil to make aluminum PCB.


Opening: opening is the process of cutting a piece of bulk into small pieces by machine according to different requirements.

The edge of the plate after the material is sharp, easy to scratch the hand, and at the same time make the board between the scratch, so after the material open the edge grinding machine.




Baking sheet:


1. Purpose of baking board:


To eliminate the internal stress of the plate during manufacture.

       

Improve dimensional stability of materials.

Remove the moisture absorbed by the sheet during storage.

Increase material reliability.


2. Baking conditions:


150 ℃ for board 4 hours, laminated thickness usually 50 mile

M a bundle of


2. Purpose of feeding

Shearing the incoming material of large size into the required size for production

3. Matters needing attention for opening materials

Check the size of the first piece

Pay attention to aluminum and copper scratches

Pay attention to plate edge stratification and sweep edge


2) dry/wet film imaging


Wet film (also known as photosensitive line oil) and photosensitive dry film are photosensitive materials. When exposed to ultraviolet light, they polymerize to form a relatively stable image.



1. Dry/wet film imaging process


Grinding plate - film - exposure - development


2. Purpose of dry/wet film imaging


The part needed for making the circuit is presented on the sheet


3. Precautions for dry/wet film imaging


Check whether the line is open after developing

Is there a deviation of the developing pair to prevent the dry film from breaking

Pay attention to poor wiring caused by friction on the board

Air residues must not be present during exposure to prevent poor exposure

After the photo exposure, the film should be stationary for more than 15 minutes before developing


Ae:


The effect of exposure is that the uv light of the exposure machine makes part of the image on the film through the negative, thus transferring the image to the copper plate.



Development:

Function of development:

Is the unexposed part of the dry film removed, leaving the part of light.

Principle of development:

The photosensitive material in the unexposed part did not undergo polymerization and was dissolved in weak base Na2CO3 (0.8-1.2%).

The polymer material remains on the plate to protect the underlying copper from etching solution.




Acid/alkaline etching


1. Acid/alkaline etching process


Etching - stripping - drying - inspection plate


2. Acid/alkaline etching purpose


After the dry/wet film is imaged, the required part of the circuit is retained, and the excess part is removed


3. Matters needing attention for acid/alkaline etching


Pay attention to poor etching and excessive etching

Pay attention to the line width and the line length

The copper surface of the coating is not allowed to be oxidized and scratched

Keep dry film clean


The effect of etching:

      

Is the unexposed part of the copper surface etched off.




4) faded film




The film on the copper surface of the protective circuit is removed by using a relatively high concentration of NaOH (3-5%). The concentration of NaOH solution cannot be too high, otherwise it is easy to oxidize the plate surface.




5) AOI process


The principle of the machine is to use the reflection effect of copper surface to make the pattern on the plate can be scanned by AOI machine and recorded in the software, and check the defect point by comparing with the data graph data provided by the customer. Defects such as open circuit, short circuit and poor exposure can be checked by AOI machine.




6) brown


The function of brown chemical sequence is to coarsen the copper surface, increase the combined area and increase the surface binding force.





7) clamp


Process description: the pressure plate is a semi-solidified sheet that connects the outer copper foil to the inner layer and each inner layer to the inner layer.




Process principle: with the characteristics of semi-solidified sheet, it melts at a certain temperature and becomes a liquid filled graphic space, forming an insulating layer. After further heating, the insulation layer is gradually solidified to form a stable insulating material. At the same time, each layer of each line is connected into a whole multi-layer board.


What is a semi-curing tablet (PP)?


Prepreg is an abbreviation of Prepreg.

It is a kind of sheet bond material synthesized by resin and glass fiber carrier.


Resins - usually macromolecular polymers, a hot - solid material.

The current commonly used is epoxy resin FR-4.


Outer process


Eight) drilling




1. The process of drilling


Drill pin - drill - test plate


2. Purpose of drilling


Position drilling of the plate to assist the following production process and customer assembly


3. Precautions for drilling


Check the number and size of holes

Avoid scratching the sheet material

Examine the flanges of the aluminum surface, hole position deviation

Timely inspection and replacement of drill heads

The boring hole is divided into two stages, one drilling: the drilling after the material is made is the peripheral tool hole;


Second drilling: the tool hole in the unit after resistance welding




Characteristics of aluminum base plate drill nozzle


The chip discharge space of the high-order bit is large: the chip discharge resistance is small, chip discharge is smooth, the heat of drilling is small, and the drilling pollution is reduced;


Thanks to nanotechnology and advanced grinding technology, the cutting edge of the drill bit is sharper than before, reducing cutting force, cutting rate and improving hole wall quality.


Design of tools based on customer application: the variety of drills is rich and can meet different application requirements.

All the parameters of the drill bit, such as drill core thickness and drill core taper, are carefully designed and effective.


Rigid symmetry of the machined edge: good for efficient cutting and avoid drift of borehole.




9) copper plate plating


A conductive metal layer is deposited in the hole of the plate after drilling by chemical method, and the metal layer is thickened by whole plate electroplating method, so as to achieve the purpose of metallization in the hole and make the circuit pass through by this method


Process:


Grinding plate - removing glue slag - settling copper - plate electroplating - down procedure


Electroless Copper Deposition, commonly known as Copper Deposition, is a self-catalyzed chemical oxidation and reduction reaction. In the process of Electroless Copper plating, Cu2+ ions are electronically reduced to Copper metal. When the reducing agent releases electrons, the reducing agent itself is oxidized.

Electroless copper plating is used to metallize holes in the manufacture of printing plates to complete the wire connection between double panel and multi-panel layers.




Screen printing resistance welding and characters



1. Screen printing resistance welding and character flow


Screen - prebake - exposure - development - characters


2. Purpose of screen printing resistance welding and characters


Solder - free: protect the line that does not require soldering, prevent the solder from entering and causing a short circuit

The character: serves as a marker


3. Matters needing attention for screen printing resistance welding and characters


To check if there is any garbage or foreign matter on the board

Examine the cleanliness of the board

The printing should be pre-baked for more than 30 minutes to avoid air bubbles

Note the thickness and evenness of the screen printing

The pre - bake after the plate to fully cool, to avoid film or damage ink surface gloss

To develop the ink face down

        

V-CUT, gongs


1. Procedures of v-cut and gongs


V-cut -- gongs -- tear protective film -- strip the front


2. Purpose of v-cut gongs


Peripheral v-cut: connect the single PCS line with the sheet cutting of the whole PNL to facilitate packaging and taking out

use


Causeway board: remove any excess from the circuit board


3. Precautions for v-cut and gongs


The size of V should be paid attention to in the process of finishing v-cut


When the gongs were in causeway, the burr was caused, the gongs were deflected, and the gongs were inspected and replaced in time


To avoid surface scratches at the end


7) testing, OSP


1. Testing, OSP process


Line testing - voltage resistance testing - OSP


2. Testing, purpose of OSP


Circuit test: check whether the completed circuit is working normally


Voltage withstand test: check whether the completed line can withstand the specified voltage environment


OSP: make the wire better for soldering


3, testing, OSP considerations

How to distinguish between qualified and unqualified products after checking

So when you're done with the OSP, the placement

Protect the wiring from damage


8) FQC, FQA, packaging and shipment


1, processes,


FQC - FQA - packaging - shipping


2, the purpose,


Qc will check and confirm the product

Qc spot check and verify

Nail pack and ship to customer as required


Use of aluminum substrate for PCB


1. Audio equipment: input/output amplifier, balance amplifier, audio amplifier, preamplifier, power amplifier, etc.

2. Power equipment: switching regulator ` DC/AC converter ` SW regulator, etc.

3. Communication electronic equipment: high frequency increase ` filtering electrical ` transmitting circuit.

4. Office automation equipment: motor driver, etc.

5. Car: electronic regulator ` igniter ` power controller, etc.

6. Computer: CPU board ` ` floppy drive power supply device, etc.

7. Power module: inverter ` solid relay ` rectifier bridge, etc.

8. Lighting decoration: with the promotion of energy-saving lamps, aluminum substrate applied in LED lamps has also started to be widely used.


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