PCB cost is one of the major factors that a PCB designer has to keep in mind while designing a PCB. The design PCB cost should be kept as low as possible but certainly not at a severe compromise of quality. There are several factors affecting the PCB price like material and complexity which are factored in while designing the PCB, but some are economic factors like quantity and pairing PCB fabrication with other services of PCB vendor which are to be factored in after designing, used for reducing per PCB board cost overall. Here are some of the factors contributing to the PCB board price.
Material Affects the PCB Price Greatly
The material of the PCB is by far one of the most critical components of choosing how a PCB must be fabricated as it governs the electrical, physical characteristics, and thermal characteristics of a PCB and has a substantial share in the PCB production cost.
- Electrical characteristics
The dielectric constant and dielectric loss tangent of a material are required for calculating the net impedance and differential impedance of a trace according to which the width of the traces on PCB are calculated. For example, FR4 material has a dielectric constant of 4.5 and a dielectric loss tangent of 0.025, polyimide has a dielectric of 3.5 and a dielectric loss tangent of 0.004 and ROS4000 material (Roger’s material) has a dielectric constant of 3.2 and a loss tangent of 0.002. The materials with a low dielectric constant and a low dielectric loss tangent are more expensive and are mostly used in high-speed data applications and microwave applications where signal integrity is crucial.
- Physical characteristics
Physical characteristics include flexibility and tensile strength of the PCB which are selected according to the application of the PCB, for example, an LED strip requires a flex PCB while a PCB designed for a TV remote will most likely require a rigid PCB. Choosing a flex PCB material will increase the PCB price and has limited advanced features when compared to rigid PCBs like restriction of layers. Similarly, the higher the tensile strength, the higher will be the cost of the material.
- Thermal characteristics
Thermal characteristics include thermal conductivity, Glass transition temperature, and coefficient of thermal expansion. The thermal characteristics are decided by the kind of environment the PCB will be used in and the kind of components that are going to be placed on the PCB. While it is recommended to use materials with high thermal conductivity and glass transition temperature it also increases the PCB price. Some common materials used to make PCBs are FR4 (General purpose and mostly cheapest), PET or Polyethylene Terephthalate (Flexible), PI or Polyimide (High performance Flexible), Rogers ROS4003 (Microwave applications), Isola Tachyon 100G (High-Speed Communication applications). Please note Isola and Rogers are not material names, they are the names of the organisations that make those materials.
Complexity is a Key Factor that Dominant the PCB Board Price
The complexity of PCB is a tricky factor to handle as even a small characteristic like via size, or trace width can determine if the PCB will be considered as an advanced PCB or a general PCB for some vendors and might shoot up the PCB board price and hence must be selected very carefully while designing a PCB. Some factors affecting PCB complexity include the number of layers, copper weight, Impedance control, physical characteristics of elements of PCB, surface finishes, and aesthetics of PCB.
- The number of layers
The number of layers in a PCB greatly influences PCB price, but for many vendors, the PCB board cost increases disproportionately with the number of layers there is because the technology required for fabricating more layers requires advanced machinery, expertise, and time. For example, many PCB vendors accept up to 4 layers of PCB in standard PCB board cost and are priced at substantially less cost than a 6-layer PCB, a similar trend is seen in the PCB board price with more than 20 layers. One must use layers judicially to keep PCB cost low.
- Copper weight
While the name suggests it is a unit of weight of copper to be used, is the areal or surface density of copper used in PCB and is measured in oz/feet². More copper weight allows more current to flow without heating the PCB and increases signal integrity. A good practice is to have enough copper weight to handle 1.5 times the current load one is expecting to flow in a PCB. An increase in copper weight will also result in an increase in the PCB price. Most of the standard PCBs use 1oz of copper as it can handle 5 amps of current without heating which is more than sufficient for small PCBs.
- Impedance control
Impedance control is done on PCBs which are expected to have high signal integrity for high-speed applications. Impedance control involves the building of precise layer stack-up with very tight tolerance which fetches more engineering fees than a normal PCB. If the PCB requires impedance control then, it has to go through more test procedures which also adds up to the PCB board cost. Impedance control is not required for PCBs with less than 100MHz or around 125MHz frequency signals (assuming components utilising the data signals are close enough). Some vendors have prebuilt stack up for some standard impedance and signal integrity value for a cheaper and quicker fabrication without compromising the quality of the PCB.
- The physical characteristics of elements on a PCB
The minimum diameter of vias, minimum trace widths, and more importantly the size of the PCB have an appreciable share of the PCB price. The size of the PCB increases the cost of the other factors like copper weight and surface finishes. The bigger the PCB size, the higher the PCB price as it requires a greater portion of materials and tests. Another factor is blind via which adds up to the PCB price, but it is generally used for HDI PCB (High Density Interconnect) used in high-frequency applications. Many vendors charge for smaller traces and smaller diameter vias which require special machinery for tighter precision. Designers must be careful with the width of the trace and diameter of the vias as many vendors also levy an advance PCB board price for smaller vias and thinner traces.
- Surface Finish
Surface Finish is the layer applied on copper to provide a solderable surface on the PCB to mount components. While mostly HASL (Hot air solder levelling) and lead-free HASL (which are the cheapest options) are used in many simple PCBs, some better quality PCBs utilise more expensive surface finishes like ENIG (Electroless Nickel Immersion Gold) for finer pitch components and durability and hard gold for high-quality contact points. One of the most expensive surface finishes is NEPIG (Electroless Nickel Electroless Palladium Immersion Gold) for ultra-fine pitch components and extreme durability. One must choose a surface finish according to the environment of the PCB where it is to be used, the pitch of the components, an estimate of the number of times a component may have to be resoldered on a PCB, the expected lifetime of a PCB, and environmental standard.
- Aesthetics of the PCB
Like the colour of the material of the PCB other than green, the addition of the manufacturer’s logo hiding or removal of vendor’s assembly number addition, edge plating, gold finger plating, and custom shapes all add up to the PCB board price though not as substantial as the previously mentioned factors. One must certainly not ignore the aesthetics of the PCBs that are going to be exposed without a casing or for direct industrial or commercial use.
Quantity has a Significant Impact on PCB Price
The order quantity of the PCB is to be factored in post-designing of the PCB. The quantity has a very straightforward relation with the PCB board price, more number of the same PCB in one order will result in less PCB board price simply due to economies of scale and distribution of setup cost on each PCB. Bulk order also gives leverage for the customer for a discount.
We can ask PCB manufacturers to quote different price breakdowns as prototypes, small series production and mass production, to choose the best economic options.
Other Factors Which Affect the PCB Price
Other factors like lead time, opting for fabrication with assembly and components turnkey, and opting for cheaper logistics all reduce the cost of overhead charges levied on PCBs and are sometimes also entitled to special discounts.
Besides, other tactics like repeat orders and better vendor relationships also open up the possibility for loyalty discounts.
Conclusion
Many more factors might vary from vendor to vendor along with all the above-mentioned factors that contribute to the PCB board price. A combination of efficient and smart design and well-handled economics is essential for the net PCB board cost. While it is certainly not easy the first time but with experience and interactions with vendors one can have good control over PCB manufacturing cost and quality compromise.
