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Hard Cost Drivers in PCB production

by Ruben Contreras, Program Manager - NCAB Group USA

One topic that always seems to be on everyone’s mind is what drives the cost of a circuit board. NCAB has multiple presentations on different subjects and this one remains at the top of the list of customer requests.

Where do costs originate? Well, 80-90% of all costs are built into the project in a very early stage of the chain – before suppliers (EMS companies, PCB suppliers, etc.) have sight of the design.

Description of where the basic costs for a PCB originates

We always recommend involving your suppliers very early in the design stage. In order to tackle the subject. We have divided the cost drivers into two categories, the “Hard Costs” and the “Soft Costs” drivers in PCB production

Today we will discuss the Hard Cost Drivers. There are the basic factors, such as the size of the board — we all know that the larger the board size, the more material will be needed and thus increase the cost.  If we consider a basic 2 layer board with a 2×2” dimension as our ‘baseline’, increasing the dimensions to 4×4” will quadruple the initial material cost.  The material demand is not only a factor in the X and Y axis but also in the Z axis as increasing layer count also impacts the base material cost.  This is because every core added to a stack up will require added material, plus the cost of processing the material, printing and etching, AOI inspection, chemical cleaning and oxide process. Increasing the number of layers increases the cost of the finished product.

The material you choose will also impact cost. Basically, any requirement beyond the standard FR-4 will add cost to the board, and requiring a very specific material will add cost and may create problems with availability. I usually recommend referencing IPC4101/ XXX as your default callout, or if you are specifying a specific material, I always recommend you include an ‘or equivalent’ option — this will allow factories some options on which materials to use while still meeting your requirements.

Discuss copper Thickness?

The build complexity would be the next culprit adding cost. When you take a standard multilayer board and add in blind vias, buried vias, or a combination of both, you are adding cost. What engineers need to understand is that you are not just adding drilling cycles to the board, you are actually adding bonding cycles also., In order to produce the buried vias the board has to be bonded, drilled and plated, then bonded again for the next drill and plate cycle. The more cycles the board has to go through, the more the cost increases to produce it.

Illustrations showing different plating and bond cycles in a PCB

Another very important factor to consider is the array. How you panelize the board will affect the material usage. Some designers will leave a lot of space between boards and large tabs. When this is not needed it is just adding to the real estate of the board and thus, as I illustrated previously, cost. Reducing space between boards and the size of the tabs will reduce how much material is used and this translates to actual cost savings. If the design is square or rectangular, creating an array with v-score and “0” spacing will provide the ultimate savings. Having rails on two sides instead of four will also increase the savings.

Different versions of panelisation

Track and gap will also impact price. Different factories will have different capabilities as to how small a track and gap they can handle — but rule of thumb is the same, the smaller the track and gap the more difficult it is to produce, increasing  the fail rate. This becomes even more of an issue if the design is one where the tracks are very long or in loops. The longer the trace the higher the possibility for failure. If finer tracks and gaps are necessary, factories require advanced equipment and capabilities which ultimately also leads to an increase in cost.

Hole quantity and size is another cost driver. Having very small holes, or too many holes results in a more expensive board. Smaller drill bits have smaller flutes which will limit the amount of boards that can be drilled in a drilling cycle.  Additionally, due to the small flute length the PCB fabricator is limited in how many production panels can be drilled in a stack, which contributes to an increase in labor cost because of additional cycles required on the CNC drill machine. You should also consider the aspect ratio. Drilling small holes into thick boards will be a cost adder and may limit the number of factories that can manufacture your design.

The final process in the Hard Cost Drivers that we have to address is the surface finish. Adding hard gold, thick gold or specialty finishes such as ENEPIG will add to the cost. We all know precious metals are costly, and adding them as a finish will undoubtedly add cost to the board.

When it comes to Hard Cost Drivers the idea is to only spec what you actually need. Do not ask for a finish that is not required, or materials that are not necessary. All the choices you make in the design phase will impact the final price of the board. What I always recommend is to get your board supplier involved as early as possible in the design of a new product. As you can see, there are many choices to be made — if they are not addressed at the right time, when the design gets to the fabricator it will already be too late to propose changes. Doing so at this stage will only add delays to the production cycle.