Whether you are designing (PCBs), building (an office building), or baking (a cake), extra stacks, stories, or layers cost more. In regards to PCB design, however, it is not as simple as asking for extra icing between the sheets of a cake.
There are several factors that one must consider to arrive at a cost per layer or stack pricing. However, to make any comparisons, you must also have an understanding of the assembly process, design constraints, and the cost constraints that determine if you are building a 4-layer, 6-layer, or 8-layer PCB.
Over the next few paragraphs, we will discuss these factors that warrant the need for extra layers and the costs associated with building multilayer PCBs.
What Determines PCB Manufacturing Costs?
PCB design requires a substantial level of intricacy, precision, and accuracy. When considering build cost, it is dependent on your design and PCB end-use. In other words, if the PCB in question is for general or daily use, then the cost will be substantially lower than say if it was for a high-tech application.
However, this is only a broad overview assessment of PCB cost-affecting factors. In reality, there are several real-world factors that affect PCB cost. In general, the three most impactful factors that affect PCB manufacturing cost are the size of the board, the number of layers, and the type of material the manufacturer uses.
In the next few paragraphs, I will discuss all of the common factors one must consider when determining PCB manufacturing costs.
The Eight Factors that Determine PCB Cost in Detail
The following are the eight determining factors one must consider when gauging PCB manufacturing cost, be it a 4-layer, 6-layer, or 8-layer design.
The Choice of Materials the Manufacturer Will Use to Produce the PCB
This first one is rather obvious since the type of manufacturing material in use affects the cost of nearly everything within every industry. For example, when addressing the interior of a car, the leather seats cost more than the fabric or cloth material. Therefore, it is understandable that this same principle applies to PCB manufacturing, as well.
Also, as you may know, a typical PCB is laminated with FR4 (flame retardant 4) material, but this will not suffice for PCBs made for high-intensity use, for example, in the fuel or aerospace industries.
Here are the factors that will influence your material selection process:
Thermal Reliability: In general, determine the temperature expectations of the PCBs application. In other words, make sure that the temperature rating of the material you choose falls into the acceptable range.
Temperature Reliability: Again, this is dependent on the material not only functioning within a specific temperature range, but it must also do this within a controlled setting without overheating over an indefinite length of time. Keep in mind that any PCB (material) you intend to use in a high-temperature operating environment, must pass this test.
Heat Transfer: This is a requirement that points to a board's ability to withstand high-intensity heat without undue transfer of said heat to the attached or adjacent components.
Signal Performance: As the name suggests, this entails whether a material can facilitate uninterrupted electrical signals throughout each operating cycle. As you may know, this is critical to PCB functionality.
Mechanical Properties: This deciding factor is a focus on the material’s ability to withstand the foreseeable physical stresses of its applicational use.
Selecting the proper material for your circuit board can drastically effect durability, sustainability, and lifetime
The Actual Size of the PCB Itself
I am sorry to say it, but size does matter, especially when considering costs. The size of the PCB you require will affect its final cost. This is equally true when considering its panel utilization. These are two of the more critical factors that affect the overall price of the PCB.
Note: In general, the number of circuits you require for your particular application or design will determine board size.
The Number of Layers or Stacks in Your PCB Design
As I eluded to earlier, the more layers, the higher the cost. This, of course, is also one of those distinct determining factors of price. These increases are also in consideration of the size and types of materials the manufacturer uses in its production as well.
Here is a general comparison of the cost increases:
1-Layer to 2-Layers: (35% to 40% cost increase)
2-Layers to 4-Layers: (35% to 40% cost increase)
4-Layers to 6-Layers: (30% to 40% cost increase)
6-Layers to 8-Layers: (30% to 35% cost increase)
8-Layers to 10-Layer: (20% to 30% cost increase)
10-Layers to 12-Layers: (20% to 30% cost increase)
One of the most significant price increases in the manufacturing process occurs when you add a second layer. This is understandable since we know that this increases the number of production steps (lamination process). The logic here is, the more layers, the more time and resources are required to complete the manufacturing process.
The Type of Finish of the PCB
The finish you choose for your PCB design will affect the cost. Albeit, it is a minor factor; it is still a factor nonetheless. Some of the reasons you might choose one finish over another are the fact that some are a higher grade or they offer a longer shelf life.
Typical finish types (surface treatments and their unique features are as follows:
HASL: offers better solderability
LFHASL: provides better solderability
OSP: offers better solderability
IMM Ag: affords better solderability and Al (aluminum) wire bondable
IMM Sn: provides solderability
ENIG: offers solderability, Al wire bondable, and contact-surface
ENEPIG: better contact-surface, Al wire bondable, and solderability
Elec Au: is Al and Au (gold) wire bondable, better solderability and contact-surface
The Size of the Holes in the Board
The size and number of holes in the board will impact the final cost of production. For example, if the holes you require are super-thin, they will also require specialized tools to produce them. Again, logic dictates that the more holes you need, the more steps and production work it involves; hence, the increase in cost. Overall, the size of the holes in the board (design) is the most critical determining factor, in this regard.
The Minimum Trace Width and the Spacing
Ask any engineer, and they will tell you that if you want to transfer current on a PCB without overheating it or damaging it, you must have sufficient trace width. Trace width determination begins with proper design (simulation).
Regardless of board size, there is a general correlation between trace width and current carrying capacity. Although other factors affect current carrying capacity, the need for wider (thicker) traces will require more materials and work. Again, this will equate to an increase in price.
The Thickness of the PCB and Aspect Ratio
There is a rather straightforward correlation between price and board thickness. Thicker boards will cost more than thinner ones, but it also depends on the materials as well. To further elaborate, thicker materials can incur a higher cost to procure, laminate, and form into a PCB. This is especially true if the design you are seeking is more intricate.
The Addition of Custom or Unique Specifications
The added cost of more intricate designs is a given, and this is also true of custom or unique specifications. These types of design requirements cost more to produce because there is more work, materials, and possibly specialized tools involved in the manufacturing process. However, the use of simulation could yield a much better understanding of your possible board cost and subsequent design requirements before arriving at any final design decisions.
While it seems like a lot to consider, ultimately your job is to produce the best circuit that fulfills the device’s needs as you can.
The cost considerations for PCBs are numerous. The advice here is, take each one of these possible determining factors into careful consideration before making any budgeting decisions. The rule of thumb is, the more you require by size, layers, or design requirements, expect the cost to increase.
When considering working on 4-layer, 6-layer, 8-layer or any number of layer PCB, Cadence’s suite of design and analysis tools will assuredly be able to make your process easier. Utilizing Allegro PCB Designer will make both the manufacturing output and easy process, as well as taking care of DRCs and stackup necessities with clarity and ease.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.