I love cooking for large gatherings. Cooking for friends and loved ones is among the most meaningful expressions of warmth and gratitude. A few years back, at Thanksgiving, we were tasked with cooking dishes that adhered to multiple diets and allergies. While it was challenging to coordinate recipes between each person’s restrictions, it was ultimately gratifying to discover some new favorites that I otherwise would’ve passed over.
In some ways, high-volume PCB production is a bit like potluck cooking in that some reasonable sacrifices might need to be made for universality and cost. Also, like cooking, PCB development cycles rarely appear perfect on their first attempt. Instead, the design adopts a method of revision to evolve from the prototype to the final product steadily.
The Processes of PCB Production
Manufacturing isn’t a one-shot progression from design to product. Instead, it’s a nested cycle of iterations that sequentially mature a product into its final form. As with any engineered device, pre-design begins as an idea, but an existing product may be adapted, whether internal or external. In the latter cases, much of the design legwork has been accomplished. However, design teams will still want to carefully evaluate how any additions or subtractions to the board may affect its performance or function.
Each step contributes immensely to the success of the final product:
- Design conception covers the initial stages of product functionality, i.e., what does it do differently or better than existing products? This process may not even center the circuit functionality but rather on how to capture performance within a specific form factor for portable or wearable devices.
- Proofs-of-concept shows the validity of a design but not necessarily its ease of producibility or feasibility. It is a crude mock-up (relatively speaking) of the final design only to show it is possible.
- Circuit modeling allows designers to create a digitized representation of their circuit. This step will be integral for simulation, it can also double as the schematic when production proceeds to the layout phase.
- Simulations will be used to verify that circuits, at least theoretically, function as intended. Initial adjustments to resistance values, capacitance, etc., can be made here, as well as the logic of the circuit or circuit assembly.
- Cost Assessment is arguably the first stage of actual production. The most well-engineered designs that can’t pass analysis will need to reverse course and incorporate budgetary concerns into the design, whether that’s an adjustment to the quality of components, the number of features, or general performance.
- Layout mediates the circuit design and physical constraints of materials and manufacturing. Designers will begin by gauging specific characteristics and features of the board, such as its size, thickness, layer count, trace width, via diameter, and so on. The individual components will be placed and then connected to maximize space and performance while adhering to any design document instructions.
- Design review checks the completed layout board file to determine its viability before any manufacturing level occurs. While most of this can be automated by the rule check component of software packages, intricate, difficult-to-build, or expensive prototypes may require a more hands-on approach.
- Manufacturing translates the files and artwork created from a completed board file into the bare board and populated assembly. There are numerous complex processes under the manufacturing umbrella, and defects or lower-than-expected yield may signal a board needing optimization in its layout that should be amended before any additional work is performed on the shop floor.
- Testing co-occurs throughout the manufacturing step as it makes more financial sense to catch defects as soon as possible. Still, it ultimately serves as an evaluation of the whole finished product. Testing checks the board’s mechanical, electrical, thermal, and chemical parameters, ensuring its adherence to multiple standards while maintaining operation under stress.
A board is unlikely to complete testing without a single revision. Even if that were the case, designers should strongly consider reevaluating designs to minimize per-board cost. The layout-review-manufacturing-testing loop will continue to iterate until design teams are confident their board succinctly captures its originating design intent.
Cost Analysis for PCB Manufacturing
As form follows function, product design must be tailored to its end manufacturing goal. Prototypes and small quantity lot sizes can be less discerning in eliminating cost when quality or turnaround time needs to be prioritized. However, the larger the lot size, the greater the financial gain from eliminating redundant or extraneous features.
Layout designers can target some of the following areas:
- Layer count: The two major factors impacting layer count are the area of the board (since this defines the extent of each layer) and the density of the circuitry, the latter of which, in turn, can be impacted by the trace width and through hole via diameter parameters. In general, the greater the layer count, the worse the yield. Reducing the layer count, when possible, has several knock-on effects. Through hole via diameters can be reduced by relaxing the aspect ratio restriction, and lamination becomes simpler, especially valuable in the presence of microvias. Accomplishing a reduction in layer count is a monumental goal for any board revision, and it must be done so carefully. Routing on split planes is possible, provided the routing does not significantly divide or neck down a copper plane. It should not cross over multiple planes (which will create the potential for electromagnetic interference owing to a circuitous return path).
- Via count: The fewer vias, the better. The savings on labor and equipment wear for a dozen vias may not seem like much, but this value can become significant when multiplied across thousands of boards. Reducing processing time also aids in turnaround time for large quantity lots.
- A general reduction in manufacturing complexity: Manufacturing speed and yield increase the closer a design adheres to standard and straightforward processes. Are microvias and via-in-pad necessary, or can the layout be simplified to eliminate their need? Is a single-side assembly possible?
Your Contract Manufacturer Covers All Levels of Production Volume
PCB production focuses on actionable steps to transform an idea into a realized board. Throughout the course of doing so, certain attributes may be emphasized or deemphasized better to match a design to its role in manufacturing. Design for manufacturing (DFM) encompasses many methods. While general best practices will apply to most boards, more specific alterations will be needed to maximize yield, performance, and cost, given the constraints of the design.
PCB production can seem like an impenetrable fog, but it doesn’t need to be when you partner with a contract manufacturer with over 40 years in the industry. We here at VSE have a straightforward belief: we want to combine our engineers’ experience to build electronics for customers. Teamed with our valued manufacturing partners, we aim to maximize performance and yield while minimizing cost, whether for NPIs in San Jose or our high-volume production facilities in Reno.