Introduction
Printed circuit boards (PCBs) form the backbone of all electronic devices and equipment. From smartphones to industrial machinery, PCBs provide the platform to mount and interconnect electronic components using conductive tracks and pads. While traditional PCBs use insulating substrates made of materials like FR-4 (glass reinforced epoxy), there has been a rising demand for aluminum PCBs in high power applications.
Aluminum PCBs offer several advantages over traditional FR-4 PCBs:
- Excellent thermal conductivity allowing efficient heat dissipation
- Higher current carrying capacity
- Better electromagnetic interference (EMI) shielding
- Cost savings from reduced number of layers
This article provides a detailed overview of the manufacturing process steps involved in fabricating aluminum PCBs.
Aluminum PCB Manufacturing Process
The fabrication of aluminum PCBs follows similar steps as FR-4 PCBs but also requires specialized techniques to handle the unique properties of aluminum. The key stages in aluminum PCB manufacturing are:
1. Design and Layout
As with any PCB, the first step is design and layout of the board. The design is translated into gerber files containing images for each layer – silkscreen, solder mask, copper layers etc. The minimum design rules for trace width, spacing, hole size etc. are more relaxed for aluminum PCBs allowing heavier copper and easier routing.
2. Material Selection
The aluminum substrate or base material is selected based on thermal and electrical requirements. Popular options include:
- Aluminum alloy 5052 – Good electrical conductivity and corrosion resistance
- Aluminum alloy 6061 – High thermal conductivity and easy machinability
- Aluminum alloy 7075 – Highest strength among aluminum alloys
The substrate thickness typically ranges from 1.6 mm to 6 mm.
3. Surface Preparation
The surface of the aluminum substrate must be prepared to enable proper adhesion of the copper foil and other coatings. This involves:
- Degreasing – Removal of oils and organic contaminants using solvents
- Desmutting – Removal of aluminum oxide layer using acidic or alkaline etchants
- Texturing/Roughening – Creating microscopic unevenness on the surface through chemical or mechanical techniques
Mechanical scrubbing, chemical etching, and acid dipping are commonly used surface preparation methods.
4. Direct Bond Copper (DBC)
The aluminum substrate is clad with a thin copper foil known as direct bond copper (DBC). Oxygen-free high thermal conductivity (OFHC) copper with thickness of ~0.2 mm is commonly used. The DBC foil and aluminum substrate are stacked and heated to around 500°C under pressure. This allows copper atoms to diffuse into the aluminum surface, creating a metallurgical bond.
5. Imaging/Etching
The copper layer is coated with a photoresist and then exposed to UV through the phototools created from the PCB design. After developing the resist, the exposed copper is etched away to create the desired circuit pattern. This imaged PCB panel then undergoes various finishing processes.
6. Applying Solder Mask and Silkscreen
A solder mask layer is applied over the copper circuitry to prevent solder bridging between pads during component mounting. Openings are created in the solder mask at locations requiring soldering. Silkscreen layer printing identifies components placement and polarity information.
7. Drilling and Plating
Holes are drilled at locations requiring electrical interconnections between layers. The walls of the drilled holes are electrolessly plated to make them electrically conductive. Copper, silver, or gold plating is commonly used.
8. Panel Sizing and Routing
The large PCB panel is mechanically routed to divide it into individual PCB units of the required size. Breakaway tabs may be left to hold the PCBs in the panel for easier handling.
9. Testing and Inspection
Each completed PCB goes through final testing and inspection. Parameters like electrical conductivity, hole plating, component fit, etc. are verified. Automated optical inspection (AOI) systems may be used.
10. Panelization
For assembly, the PCB units are arranged in a panel frame with score lines separating the individual boards. This allows automated assembly of multiple boards in a single panel.
11. Assembly
The components are soldered on the PCB either manually or using automated surface-mount assembly lines. After soldering, the panels are broken into individual boards.
Key Differences from FR-4 PCB Fabrication
While the aluminum PCB fabrication process broadly follows the same steps, some key differences compared to standard FR-4 PCB manufacturing are:
- Special surface treatments required for aluminum substrate
- High temperature and pressure bonding of copper foil
- Relaxed design rules allow thicker copper weights
- Aluminum substrate cannot withstand high temperatures, so special soldering is required
- More flexible and ductile materials used for drilling and routing aluminum
Advantages of Aluminum PCBs
Some of the major benefits of using aluminum PCBs over standard FR-4 boards:
- Excellent thermal performance allowing heat dissipation up to 5X better
- Improved thermal management enables higher power circuits
- Lower electrical resistance provides higher current carrying capacity
- Better EMI and RFI shielding due to conductive enclosure
- Cost saving from fewer layers compared to FR-4 boards
- Simpler circuit routing with relaxed design rules
- Vibration and shock resistance
Applications of Aluminum PCBs
Some typical applications where aluminum PCBs provide advantages over traditional boards include:
- High power LED lighting
- Power electronics and inverters
- Automotive electronics
- Industrial motor drives
- Power supply units
- RF and wireless infrastructure
- Military and aerospace systems
Aluminum PCB Manufacturers
Some leading companies providing aluminum PCB fabrication services include:
- Advanced Circuits
- ASCENT
- Innovative Circuits
- METAL ETCH SERVICES INC.
- Rigid-Flex
- FastLine Circuits
- Sierra Circuits
- Sunstone Circuits
These vendors offer aluminum PCB production in low to medium volumes catering to prototyping and small-medium production runs.
Summary
Aluminum PCBs offer distinct advantages for thermal management, high power, and high frequency applications. The fabrication process requires specialized techniques like copper bonding, surface treatments, and adapted imaging and drilling processes. With growing adoption, aluminum PCBs continue to replace conventional boards in an increasing number of high performance electronic systems.
Frequently Asked Questions
What are the key benefits of aluminum PCBs compared to standard FR-4 PCBs?
The main benefits of aluminum PCBs are excellent thermal conductivity to dissipate heat efficiently, higher current carrying capacity, reduced EMI/RFI, vibration/shock resistance, and cost savings from fewer layers. This makes them suitable for high power, wireless, automotive, and other demanding applications.
Why is surface preparation important in aluminum PCB fabrication?
Surface preparation through processes like degreasing, etching, and texturing enhances adhesion between the aluminum substrate and copper foil. This improves bond strength and prevents delamination or separation during thermal cycling or mechanical stress.
What are some common aluminum alloys used as substrate for PCBs?
Some popular aluminum alloys used are Alloy 5052 for its good electrical and thermal conductivity, Alloy 6061 for thermal performance and machinability, and Alloy 7075 for very high strength. The choice depends on thermal, mechanical, and electrical requirements.
How is the copper layer bonded to the aluminum substrate?
Direct bond copper (DBC) foils are stacked onto the aluminum substrate and heated under pressure to 500°C or higher. This causes interdiffusion between the copper and aluminum, creating a metallurgical bond.
What are some key design considerations for aluminum PCB layout?
Aluminum PCB design rules allow thicker traces, larger vias, increased spacing, making routing easier. Thermal management and heat dissipation paths need to be considered. Minimal or no through-hole vias are preferred.
8 Steps to Explain a Perfect Aluminum PCB Manufacturing Process
I) Cut Lamination
1. The process of Cut Lamination
Picking – Sheets Cutting
2. The purpose of Cut Lamination
Cut large sizes of incoming material into the required size for production
3. Precautions for Cut Lamination
A. Checked for the first piece size
B. Pay attention to aluminum scraping and copper scraping
C. Pay attention to blister
II) Drilling
1. The process of drilling
Eyelet – Drilling – Inspection board
2. The purpose of drilling
Positioning the plate for drilling provides assistance for subsequent production processes and customer assembly
3. Precautions for drilling
A. Check the number of holes and the size of the holes
B.avoid the scratching of the sheet
C. Check the burr of the aluminum surface, the hole deviation
D. Timely inspection and replacement of the drill tool
E. Drilling is divided into two stages, first drill: Drill the tooling hole after Cutting Lamination. Second drills: drill the tool hole in the unit after solder mask
III) Dry/wet film imaging
1, Dry / wet film imaging process
Grinding plate – film – exposure – developing
2. Dry / wet film imaging purposes
Presenting the parts needed to make the circuit on the sheet
3. Dry / wet film imaging considerations
A. Check if there is an open circuit after development
B. Whether there is deviation in the development alignment to prevent the generation of dry film
C. Pay attention to the bad circuit caused by the surface Scratch
D. There should be no air residue during exposure to prevent poor exposure
C. After the exposure, it should be still for more than 15 minutes before developing.
IV) Acidic/alkaline etching
1. Acid/alkaline etching process
Etching – Stripping – drying – inspection board
2. Acid/alkaline etching purpose
After the dry/wet film is imaged, the required circuit portion is retained, and the excess portion circuit is removed.
3. Acidic / alkaline etching considerations
A. Note that the etching is not clean, excessive etching
B. Pay attention to circuit width and space
C. Copper surface is not allowed to have oxidation, scratching phenomenon
D. Stripping to be cleaned
V) Solder mask and silkscreen process
1. Solder mask, silkscreen process
Silkscreen – Precure – exposure – development – Legend
2. The purpose of solder mask and silkscreen the purpose
A. Solder mask: protect the circuit that does not need to solder, prevent tin from entering the short circuit
B.Silkscreen: play a show role
3. Solder mask, silkscreen notes
A. Check the board for any rubbish or foreign objects
B. Check the cleanliness of the stencil
C. After silk screen printing, Precurefor more than 30 minutes to avoid bubbles on the circuit.
D. Pay attention to the thickness and uniformity of silkscreen
E. Precure plate should be completely cooled to avoid sticking to the film or destroying the gloss of the ink
F. The ink is placed face down when developing
VI) V-CUT, Rout out
1. V-CUT, the process of the rout out
V-CUT – rout out – remove protective film – rout burr out
2. V-CUT, the purpose of the rout out
A. V-CUT: The single PCS and panel connect a little, it is easy packaging and separate.
B. Rout outboard: remove the excess part of the board
3. V-CUT, the considerations for the rout out
A. Pay attention to the deep of V during the V-CUT process, the defects of the edges, burrs
B. Please pay attention the burr, rout Deviate, checking and replace the tool in time
C. Finally, avoid scratching the board when removing the burr.
VII) Electronic test, OSP
1. Test, OSP process
Circuit test – withstand voltage test – OSP
2. The purpose of OSP and E-test
A. Circuit test: check if the completed circuit is working properly
B. Withstand voltage test: test whether the completed circuit can withstand the specified voltage environment
C. OSP: Make the circuit be better soldered
3. Testing, OSP considerations
A. How to store qualified and defect products after how to distinguish after testing
B. After the OSP is placed
C. To avoid damage to the circuit
VIII) FQC, FQA, packaging, shipping
1. The process
FQC – FQA – Packaging – Shipping
2. Purpose
A. FQC checking overall board and confirms the product
B. FQA sampling verification
C. Package and ship to customers according to requirements
3. Pay attention
A. FQC pays attention to the confirmation of the appearance during the visual inspection, making a reasonable distinction
B. FQA really checks and verifies the inspection standard of FQC
C.to confirm the number of packaging, to avoid mixing, wrong board and packaging damage
Aluminum substrate storage conditions
Aluminum PCB substrates are generally stored in a dark, dry environment. Most aluminum substrates are prone to moisture, yellowing and blackening. Generally, they should be used within 48 hours after opening vacuum packaging.
