Wednesday, May 23, 2018
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Understand Total Cost of PCB EMS Ownership
Manual assembly lines rely on PCBs that are within the specified parameters.

Electronics manufacturing services (EMS) suppliers are vital for maintaining efficient electronic production lines, but the costs and values of such EMS suppliers can be easily misunderstood. For example, changing a printed-circuit-board (PCB) supplier can be more costly than expected if all of the cost drivers and potential savings are not at least somewhat understood. By identifying the associated cost drivers with manufacturing PCBs, it is possible to develop a total cost of ownership (TCO) model, and a more straightforward approach to capturing real savings opportunities when building the next batch of PCBs.

Many different factors are involved in understanding the cost of building different types of PCBs. In studying the different variables and costs in manufacturing PCBs, it was possible to develop a list of 10 cost drivers which, when properly understood, can be used to reduce the costs of manufacturing PCBs. While this is not an all-inclusive list, it does cover a significant amount of the key elements that need to be taken into consideration when a PCB is being manufactured:

  • The number of layers.
  • The size of the PCB.
  • The panel utilization (percent) per number of PCBs on a working panel, where a standard working panel is 18 x 24-in.
  • The number of holes.
  • The trace width/spacing.
  • The surface finish/solder mask finish of the PCB.
  • The choice of base laminate/thickness of the PCB.
  • The copper weight/thickness used on the PCB.
  • The routing or die punching of the PCB profile.
  • The labor costs and amount of batch process steps needed to produce the PCBs.

Some of these cost drivers are fairly straightforward, such as the size of the PCB (where cost rises with increased size) and the number of layers, where more complex circuits require more PCB layers, but this also means increased cost. Panel utilization refers to the number of arrays or PCBs per array that can be produced on a working panel. This is typically calculated by the percentage of utilization, which is calculated from the total area for the PCB divided by the total panel area based on a typical 18 x 24-in. working panel. Higher panel utilization percentages mean lower overall costs. Utilization above 75 percent is considered good.

Another cost driver on PCB costs is the number of holes and variety of hole dimensions. Depending on the number of sizes and quantities, each different hole diameter equates to longer machining time, and more use of drill bits, resulting in increased costs. If hole sizes become extremely small, whereby laser drilling may be necessary, this will also add significant costs to the manufacture of a PCB.

PCB manufacturing costs are also impacted by trace widths and trace spacing: the width of the individual traces and how close they are to each other from a trace edge to trace edge can impact the cost, based on the cost of the imaging/plating equipment and process capabilities of a PCB manufacturing facility. Tighter, finer trace widths result in increased PCB production costs.

The type of surface finish on a PCB will also impact manufacturing costs, as well as the manufacturing process method used to produce the boards. Typically, lead-free hot air solder leveling (HASL) is the lowest-cost alternative, followed by immersion tin, immersion silver, organic solder preservative (OSP), flash gold, immersion gold, and thick gold. A number of alternative finishes are available, each with advantages and disadvantages that should be investigated before deciding on a particular surface finish.

The base laminate that is specified for a PCB production job can also impact costs. Unless particular requirements for a PCB dictate the use of a certain base laminate, a PCB supplier should be left to choose the laminate material suitable to meet the job's requirements, and to ensure that a required supply of base laminates is specified at the lowest possible cost.

Increases in copper weight and thickness in a PCB generally mean increases in cost. The copper in a PCB is rated in ounces, and represents the thickness of 1 oz. of copper rolled out to an area of one square foot. For example, a PCB that uses 1 oz. copper has a thickness of 1.4 mils. A PCB that uses 2 oz. copper has a thickness of 2.8 mils. The base copper thickness used, or how much the product is going to be plated to meet the required thickness, will impact the cost of the PCB. Typically the lowest cost option is 0.5 oz. copper (thickness of 0.7 mils), increasing in 1-oz. increments to 9-oz. copper. PCBs usually fall in the 1 to 2 oz. range.

The costs of routing or die punching a PCB profile can vary, since there are different methods for removing laminate material when developing a PCB's profile. The main approaches are based on routing, using a high-speed routing bit cutter to remove the laminate materials when creating a PCB profile. The other method is by producing a punch which would remove the laminate during a punch process. Typically, the punch process is a lower-cost option, but it will have some additional tooling costs to develop the punch tool.

Last on the list of 10 PCB manufacturing costs is the cost of labor, which can be significant when producing PCBs. Most circuit-board-assembly facilities incorporate a batch processing manufacturing process, which will require significant handling for each of the individual processes, as well as moving a product from process to process. When performed at manufacturing locations with lower labor costs, the unit labor costs for the PCBs will usually be less. Other factors that can impact PCB manufacturing costs include whether the board is to be produced to the level of a particular standard, such as an IPC Class 2 standard, which is generally applied to standard electronics, or IPC Class 3, which is more stringent (and more expensive), and even more expensive military standards. This is not the ultimate list of cost drivers for manufacturing PCBs, but understanding how these 10 items can affect costs can pave the way for a better understanding of how to control PCB manufacturing costs.

Contact: STACI Corp., 110 Commerce Dr., LaGrange, OH 44050 800-337-5102

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