Copare the cost of flex or rigid-flex with standard rigid PCB

PCB design engineers often ask if it costs more to build a flex or rigid-flex than it does a standard rigid PCB.  Obviously, there are inherent cost adders to both types of design so it isn’t quite a simple as an X vs. Y answer.  Below some of the information may be helpful for design engineers trying to flush out what might be the best path to take.

If we start with the assumption that the rigid PCB has been the “standard” build (and we can look at the variety of cost adders below) it might be good to determine if any of the following benefits of a flex or rigid-flex are a target of the project being considered.

Need for small/lightweight circuit
Foldable to conform to varied 3-D shapes
Better space utilization in end product
High reliability/integrated cabling (reduce the number of connectors)
High reliability during dynamic bending applications
Wide latitude of design concepts
High shock and vibration resistance
 In a rigid PCB we see four major cost drivers.  These would include:

# of layers. Each add’l 2 layers will add app. 20% based on material and lamination costs. HDI can be used to reduce layer count if HDI cost offsets layer count cost.
Hole size/# of drills will impact cost. Large # and small drill sizes will impact cost (usually staying above .25mm drill size will have no cost impact).
Spacing of hole-to-pad. Keeping a 4 mil space is normally sufficient to not warrant any cost adder.
Trace/Space. Always something to take into consideration.  If above 4/4 there shouldn’t be any cost adder.  Oftentimes, you can get to 3/3 without a cost adder but this wouldn’t be applicable across all manufacturers.
 In a rigid-flex and flex design the major cost adders would include:

Panel utilization is a very BIG cost factor for flex and rigid-flex PCB. Understanding what panel size the manufacturers use and then maximizing your design and layout to utilize as many units per panel can dramatically impact cost.
Types of material callouts for both the polyimide and cover layers may have cost impact.
Layer count of both the rigid (see above) and flex portions of the design will have a cost impact.
Types of stiffener being spec’d and surface finish callouts could have some cost impact (FR4 stiffener and ENIG on lower end of cost scale).
 Since function is the most important part of PCB design, cost factors normally don’t come into the discussion until after the design is created.  This oftentimes puts function, quality, and cost targets all at odds with each other.  With some information up front on cost drivers and having an understanding if the end product being designed is “highly” cost sensitive or not may help guide the PCB designer into the most efficient design for the product.