At Rush PCB Inc., the production of printed circuit boards (PCBs) involves so many diverse and varied possibilities that they complicate the process of estimating the factors affecting the cost of manufacturing them. Essentially, the considerations for the cost factor depend majorly on the various production strategies manufacturers use, different production equipment they employ, and the multitude of technologies available to them for creating the final product.
Irrespective of the factors responsible for the cost build up, it is essential to consider control of costs in the early phases of the PCB manufacturing process. This is because the cost of a PCB is designed into it, and it is impossible to reduce it later without re-design. Although additional process steps do add to the associated cost in terms of materials, consumables, process times, waste treatment, and energy, the process cost impacts the PCB price regardless of the manufacturer.
At Rush PCB Inc., costing in PCB fabrication depends on several variables that contribute to it through different percentage factors. The variables include the complexity of the board, the raw materials used for the fabrication, the equipment used, and the overall efficiency of the process. For ease of classification, dividing the cost factors into three categories leads to:
- Significant cost factors — Category I
- Important cost factors — Category II
- Minor cost factors — Category III
It is important to note that important and minor cost factors related to Categories II and III depend on the equipment used for fabrication and are therefore, specific to the manufacturer.
Significant Cost Factors — Category I
Major factors contributing to the cost in category I include:
- PCB size
- Yield or effective utilization of material
- Number of layers or layer count
- PCB complexity
- Materials used
This is a simple linear equation with the cost increasing linearly with the size of the PCB.
Yield or Effective Utilization of Material
Unless the unit PCB is of an excessively large size, manufacturers fit several units into a panel. Usually, panels are vendor specific and available in standard sizes such as 18x24”, 18x21”, or 21x24” and so on. Utilization depends on the area of the panel used for the PCBs, with 77% and above qualifying as good utilization. For high volume production of PCBs, panel utilization becomes one of the most critical aspects with respect to PCB cost.
Number of Layers or Layer Count
This is a simple equation with the cost increasing with the number of layers. Usually, more layers translate into additional costs because of more production steps, more material, and additional production time. However, this is not a linear increase, as converting a single layer PCB to two layers may increase the cost of the PCB by 30-40%, whereas adding two additional layers to a 10-layer PCB might increase the cost only by about 20-30%. This cost factor also depends on the complexity of the PCB design and differs from manufacturer to manufacturer.
The reverse also does not work out linearly. Reducing the layer count does not always reduce the overall cost, as reduction of layer count mostly involves more complex technology and aggressive design practices, both of which affect the yield. However, if the complexity and design remain constant, the change in cost of the PCB depends linearly to the number of its layers.
PCB complexity depends on the number of layers and the number of vias on each layer, as this defines the variations of layers where the vias start and stop on, requiring so much more lamination and drilling steps in the PCB manufacturing process. Manufacturers define the lamination process as pressing two copper layers and dielectrics in between adjacent copper layers using heat and pressure to form a multilayer PCB laminate.
As via structures majorly affect the manufacturing process, eminent fabricators such as Rush PCB Inc. optimize costs by using micro-vias and High Density Integration (HDI) technology. Not only does the HDI technology reduce the overall costs by decreasing the number of layers, it also makes the PCBs smaller, lighter, and thinner, while at the same time providing much superior electrical performance.
The selection criteria for the materials used for fabricating Printed Circuit Boards depends on several application-based factors, governed mainly by frequency and speed of operation, and the maximum operating temperature.
These factors comprise thermal stability, temperature related reliability, temperature cycle reliability, heat transfer rate, time to delamination, and many others. In fact, the higher the frequency of operation or speed of the signals, more important is the choice of materials for fabrication of the PCB. For instance, compared to the regular Phenolic FR-4 material, use of Polyimide increases the cost by about 3-5 times, but use of PTFE based microwave materials may inflate the costs by nearly 10-50 times.
Important Cost Factors — Category II
Although the cost factors involving category II are greatly dependent on the involved manufacturer, important cost factors can be listed as:
- Track and gap geometry—thinner is more expensive
- Control of impedance—additional process steps increase costs
- Size and count of holes—more holes and smaller diameters drives costs upwards
- Plugged or filled vias and whether they are copper covered—additional process steps increase costs
- Copper thickness in the layers—higher thickness means higher costs
- Surface finish, use of gold and its thickness—Additional material and process steps increases costs
- Tolerances—tighter tolerances are expensive.
Minor cost factors — Category III
These minor cost factors involving category III are dependent on both, the fabricator and the application of the PCB. They mainly involve:
- PCB thickness
- Various surface treatments
- Solder masking
- Legend printing
- PCB performance class (IPC Class II/III etc.)
- PCB contour—specifically for z-axis routing
- Side or edge plating, if any
For estimating costs accurately, experts at Rush PCB Inc. recommend taking an existing design scope and making adjustments on the requirements based on estimated technologies. Such estimates offer more relative data points for making any cost per technology decisions. The estimates also prevent later surprises in the process once resources are committed to a design.
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