Several factors influence the cost of low-volume multilayer PCB Production. Some factors are readily perceived as directly influencing the cost: producing a greater number of boards, using more vias in each board, using smaller mounting holes, vias, and traces, using more layers, and component density per board. Other factors are equally influential, but not directly evident of being so—board material, copper layer thickness and quality, surface finish, processing, and any special requirements.
However, the factors involved above do not impact the cost linearly. Moreover, some factors influence others. For instance, doubling the number of boards and components may not result in doubling the total cost of an order. Increasing the size of the board may lead to an increase in its cost, but if this reduces the number of layers, then the overall cost may decrease. In this article discuss the above factors, how they impact the cost, and each other. We will also look at how to balance the cost to performance for low-volume multilayer PCB production.
Cost Breakup for Multilayer PCBs
| Factors | 2-Layer PCB | 4-Layer PCB |
| Core Material (%) | 15 | 25 |
| Prepreg & Adhesive Material (%) | 4 | 6 |
| Internal Layers (%) | – | 20 |
| Drilling (%) | 9 | 6 |
| Plating & Finishing (%) | 35 | 17 |
| Photo Etching (%) | 12 | 7 |
| Solder Mask & Silk Screen (%) | 12 | 7 |
| Testing & Shaping (%) | 3 | 2 |
| Management Cost (%) | 3 | 3 |
| Profit Margin (%) | 7 | 7 |
The above table is an example to illustrate the difference in cost breakup for a simple 2-layer and a 4-layer board. Notice that the cost of base material goes up as the number of layers increases, and the cost of internal layers is added, which was not necessary for the 2-layer board. However, the cost of plating and finishing tends to decrease with increasing number of layers. This shows that the challenge of balancing the performance and manufacturing costs for multilayer PCBs is fairly complex.
With increasing complexity of electronic devices, it is essential to have multilayer PCBs with more components in smaller spaces. Although this increases the functionality offered by the board without compromises in its performance, the design and fabrication of these boards demand significant cost consideration. This calls for a strategic approach to factors like material selection, lead time reduction, and sustainability practices. Let us consider the roles played by these factors.
Key Factors in a PCB Quote:
Calculating low-volume multilayer PCB production costs requires considering design specifications and fabrication methods necessary to meet those requirements. Manufacturers start by analyzing factors like layout and design, layer count, minimum trace width, and hole and via sizes. Each of these elements directly influences the material to be used and the fabrication process.
1. Board Dimensions
The overall board size directly impacts its cost. This is simply because a larger board requires more raw material and fabrication time, thereby increasing the cost. The thickness of the board has a negative impact on the cost, up to a certain limit. For instance, very thin boards are more expensive, as they are more prone to damage during fabrication, and hence, must be handled with greater care.
2. Material Selection
The type of material used for the board has a significant impact on its cost. A broad classification of these materials involves:
- Standard Materials:
Standard materials for PCBs include FR-4, Paper Phenolic, and CEM. These are readily available and therefore inexpensive. It is easy to handle and process them during fabrication. These features make them very popular for use in general-purpose consumer electronic products operating in low-heat environments.
- High Tg Materials:
These materials are indispensable when operating in high-heat environments, as they do not delaminate or deform at high temperatures. However, they are more expensive as compared to standard PCB materials. Manufacturers use them in specific consumer electronic products, automotive, industrial, and military applications, especially where the environmental temperatures are high.
- High Frequency Materials:
These materials are specifically useful for high-frequency, high-speed applications, where signal integrity cannot be compromised. They are more expensive compared to standard PCB materials. These materials are very useful for communication, radar, and aerospace equipment.
3. Number of Layers
Increasing the number of layers increases the cost of the board, as the manufacturer must fabricate and process each layer separately, and then align and laminate them to form the board. However, increasing the number of layers by decreasing the overall dimensions of the board can offset the cost to some extent, but this again depends on the number of layers and vias introduced, the width of tracks, and the spacing between them. For instance, converting a 2-layer board to a 4-layer HDI board may reduce its cost, but then, that depends on its complexity and final dimensions.
4. Production Volumes
All manufactured goods benefit from scale. This is because high-volume production can reduce unit prices as it spreads the tooling and setup costs. On the other hand, small-batch orders are more expensive, as they require relatively high preparation and start-up costs.
5. Copper Type
High-speed and high-frequency PCBs require special copper foil for optimal signal transmission while minimizing losses. For this, the copper must have high conductivity, low surface roughness, and uniform thickness. For reliable high-frequency and high-speed performance, it is essential to select the appropriate type of PCB copper foil from ED or electrodeposited copper foil, RA or rolled annealed copper foil, VLP or very low-profile copper foil, and RT or reverse-treated copper foil. All these are more expensive as compared to regular copper foil.
6. Copper Thickness
The copper thickness on a PCB is typically standard, with sizes like 1 oz, 2 oz, and thicker. Higher thickness of copper means the PCB has better conductivity, which is highly desirable for high-current applications. However, thicker copper is more expensive and requires more efforts during fabrication, thereby increasing the manufacturing cost.
7. Trace Width and Spacing
Thinner widths and narrow spacing of copper tracks on the PCB require more precision during manufacturing. This leads to an increased cost. Achieving tight tolerances requires specialized equipment and more advances fabrication techniques.
8. Holes and Via Types
The PCB cost directly depends on the size, complexity, and number of drilled holes, including vias. While regular through holes and vias may be relatively inexpensive, advanced types like buried, blind, and microvias can add to the cost. Accurately positioned and small-diameter vias increase the manufacturing difficulty and, in turn, increase the board cost.
9. IPC Level
The international standard IPC-A-600 references three classes of PCBs—Class 1, 2, and 3. Manufacturing requirements grow more stringent as the class level increases. This increases the cost correspondingly.
10. Turnaround Time
If you need your PCBs urgently, be prepared to spend more. This is because quick-turn services require the manufacturing processes to be expedited, and this comes at a premium.
11. Testing and Quality Control
High-quality boards often demand strict quality control, rigorous testing like AOI or automated optical inspection, and X-Ray inspection. These are expensive processes requiring sophisticated setups, adding to the final price of the board.
12. Surface Finish
The surface finish, including solder mask and silk screen, can affect the performance and durability of a board, while affecting its price. For instance, while HASL or hot air solder leveling is relatively low cost, ENIG, Immersion silver, and others offering better durability, are more expensive.
Key Factors of PCB Design Cost
While the above primarily involve fabrication costs, it incurs one-time PCB design costs also. These include:
- Component Selection Costs
This is a very important step involving the selection of components and is measured mainly in the number of hours times the design fees.
- Schematic Design Costs
Mainly defined in number of hours times the design fees, this involves the time taken to design and draw the schematic based on the components selected.
- Simulation and Analysis Costs
This cost is calculated in hours times the design fees for the time taken to simulate the circuit and complete the analysis of its functionality.
- PCB Layout Costs
Calculated in number of hours times the design fees, this is the cost involved in laying out the PCB according to specified standards.
- Design Reviews and Documentation
This is also calculated in the number of hours times the design fees, and involves the number of hours spent reviewing the design and documenting it.
Please note, any design changes will add to the above costs, involving the number of hours necessary.
- Tooling Costs
For complex PCBs requiring additional tooling like stencils and test jigs, their one-time design and fabrication costs are distributed over the number of boards to be fabricated.
Low-Volume Multilayer PCB Production Costs
For the production of low-volume multilayer PCBs, the OEM cannot take advantage of scale to bring down the cost. However, there are other avenues the OEM can explore to bring down the costs without sacrificing the performance of the boards. Of course, the nature of the PCB’s application contributes tremendously to this decision. For low-volume multilayer boards, let us consider them in their order of preference:
- Prototype PCBs
As prototype PCBs also fall under low-volume production, they offer the maximum scope for reduction of production costs. In most cases, prototype PCBs are typically made for proving the concept. Unless the prototypes are meant for high-speed applications or flexing, making the boards with FR-4 material will bring down the cost significantly. Going for standard copper weights and PCB thickness can also help to save money, as will accepting regular track widths and spacing.
The plating and finishing processes add significantly to the PCB costs. Therefore, avoiding these processes for prototypes can result in drastically reduce the costs. Unless necessary, not covering the PCB with solder resist and silk screen printing will also help to cut down the costs.
For prototypes, drilling 0.6 mm or 0.8 mm can also help to keep costs down, as the drilling rates go up below 0.6 mm. Accepting regular turnaround times can also bring down the cost.
- Low-Volume Multilayer PCBs
In contrast to prototype PCBs, the OEM may require a greater number of PCBs, but for a small batch. As these PCBs must be complete in all respects, there is a far lower scope for cost reduction. For instance, these boards must come with solder resist, silk-screen printing, plating, and finishing, there is not much scope for reducing prices in these processes.
The best option for reducing prices, therefore, lies in selecting a low-cost material. However, if the board is to be used for high-temperature or high-speed applications, this option also becomes unavailable, as the boards must be made of high-cost material to achieve its functionality.
The only option in the above case is to procure the boards from on-shore suppliers, as this reduces the added cost of insurance, freight, and shipping if sourced from overseas suppliers.
The OEM may explore reducing the board size by increasing the number of layers and the component density. However, this is a matter of trial and error, as the price per board will be a compromise between increase in number of layers, reduction in board size, reduction in track width, and spacing.
Conclusion
As a foundation of modern electronics, the printed circuit board carries a tremendous heft in calculating the market price of the product. According to PCB Trace Technologies Inc., although balancing the cost vs. performance in low-volume multilayer PCB production is a tricky process, the scope for the exercise primarily depends on the nature of the application and the actual number of the boards.
