I sat at my desk contemplating the subject of this blog post, trace and space circuitry for printed circuit boards, and as usual, I drifted back to the start, for me, which was 1982. The date stamp amuses me – how is it 2024, already!? Of course, when you look back, you can’t stop the memories from flooding in.
Let’s return to the 1980s for just a minute. Besides great big hair, rock and roll, fast cars, long hot summers, and, oh, living near a recording studio that hosted bands like the Rolling Stones, Aerosmith, and The J. Geils Band. It was amazing! We got to sneak through the fields and listen to them rehearse; it was the best time. I also started my first real job manufacturing printed circuit boards (PCBs) in Central Massachusetts (sorry, back to circuit boards). We used to pump out boards for IBM, Texas Instruments, Intraplex, WelchAllyn, AcTech. There were so many big-to-us companies.
There were thousands of panels with circuit widths you could drive a truck on. I would bet at least nothing less than 0.010 mil for most of the 80s with a sprinkle of 0.008 mil. In general, there was nothing we couldn’t build then. Long days, plenty of overtime, and even forced weekend shifts – I’m tired just thinking about it.
Trace and space, on most PCB designs then, were on 0.5/0.5oz copper and plated up. Inner layers were mostly ½ oz copper, so, yes, all day we could manufacture this type of technology with minimal manipulation. The technology was slowly developing through the 80s, and when we saw more multi-layer PCBs with thinner trace and space, 0.007 mils was more common. More layers and the parts themselves were changing size, shape, and thickness.
PCB with trace and space greater than 0.010 mils.
PCB Design: What You Need to Know
In today’s PCB design world, with everything smaller or more complex, the days of easy-to-process circuitry are gone. We receive complex files all day long and requests for quotes for production. We are looking at the data for a good drawing with details, confirm costing attributes, and do our best to catch all the undefined details. Trace and space are seldom specified within the PCB fabrication documents unless it is for impedance controls. Even then, some of the details are not brought to the forefront to avoid cost increases.
Most common designs have 0.007 mils and less (more towards 0.005 mils), and more frequently, 0.004 mils. It is no secret that we are pushing technology levels, but I often wonder what we are doing ahead of routing and layout. Is manufacturing even a forethought? It certainly should be!
PCB with trace and space less than 0.005 mils.
PCB Design Basics
Some basics to think about: circuit width and spacing should not be equal. The tighter and more complex the PCB is to lay out, the sooner customers should consult with the raw board manufacturer.
Consider the manufacturing process, and if you are not sure, then consulting during routing layout is a must. When parameters are set in the data set with 0.005 mil trace with 0.005 mil space and bundles of traces have no room for modification, it is more difficult to process the product.
Operating equipment at a zero loss is difficult. There are specifics to think about. For example, a 0.005 mil line on 0.5 oz copper without modification manufacturing must be perfect and have no loss in linewidth. Although possible, standard manufacturing processes with tolerances and a little wiggle room in design and routing allow for ease of production, less fallout, and better cost.
Processing PCB Data to Allow for Etching
When designing the PCB, allow for additional space between copper features. A 0.005 mil trace with 0.006 mil space minimum setting allows manufacturers to add an etch factor, even .0055 allows manufacturing to have some play room.
What Is An Etch Factor?
An etch factor is the increased amount in the trace width to allow the copper thickness to be processed without the loss of desired trace width.
With etch compensation, a 0.005 mil trace on 0.5 oz copper would be increased to 0.0055 mil or 0.006 mil if there was adequate spacing.
Think of it this way: 0.005 mil wide trace, 0.5 oz copper, which is 0.0007 mils thick, that’s a lot of copper to etch through to the laminate surface and hold the tiny trace width. Using a 0.005 mil trace with 0.005 mil space will allow for minimum trace increase to allow for processing.
I mentioned bundling circuits. This is when layout and routing will place consecutive circuits 0.005 mils apart in groups. In many cases, we can align the bundle and increase the space a little 0.0005 mils (even 0.00025) allows for some processing consideration. That same bundle, had it been laid out using 0.0055 mils or 0.006 mil spacing, would have consistently processed without issues. We have seen 0.005/0.005 mils or even 0.004/0.004 mil line and space requested to be produced on 1 oz copper, to control this process and produce this high technology. As copper weight increases, the need for room to compensate for circuitry is most important for manufacturing.
Testing the Limits
When circuit board design and layout do not consider manufacturing, it tests the limitation of processing, manufacturing equipment, and normal production settings. Per IPC manufacturing processing, tolerances and acceptability should be considered during the early development of the design. The end goal is to develop a product that is reliable from prototype to production. Making the right decisions from the start allows for consistent repeatable production with a low risk of fallout. When considering the design, knowing what is needed for the circuit and space-to-copper weight ratios is the base of your success. Transitioning from prototype to production with a solid manufacturer is key to cost savings, fewer revisions, and quicker to-market products.
PCB manufacturing in partnership with contract manufacturing is key to end product assembly, it is just as important or more important to have a strong relationship between Electrical Engineer Designer and PCB manufacturing so enlist their assistance early on. Consult engineering for manufacturing, consult contract manufacturing, and work with a team that can support you from concept to production. Epec has implemented free services to aid in the ease of the process. Design assistance with professional resources, and free DFM with engineering staff to make suggestions for improved yield. Knowing your PCB team has had a first look or suggestions for best-practicing production is a plus.
Summary
Epec has resources across the globe; domestic and offshore capabilities support all production needs, including domestic, ITAR support, PCB design, layout and a routing specialty group to produce top-notch data for producing quality products.
Utilizing our always-free DFM process to troubleshoot potential pitfalls during development, saves you cost and time to market. We know time spent can be dollars lost, which is why we activated specialty teams to curb known issues.
Key Takeaways
- PCB Trace and Space Design Evolution: Modern PCBs have significantly reduced trace and space dimensions, now commonly as small as 0.005 mils or less, compared to the wider traces of the 1980s.
- Importance of Manufacturing Considerations: Early collaboration with PCB manufacturers during design and routing is crucial. Consulting them helps ensure manufacturability, reduces fallout, and optimizes production costs.
- The Role of Etch Factors: Incorporating etch compensation into designs allows manufacturers to maintain trace width consistency despite copper thickness, improving production reliability.
- Spacing Adjustments Improve Yield: Slightly increasing space between bundled circuits (e.g., 0.0055 or 0.006 mil spacing) eases manufacturing, reduces errors, and ensures better product quality.
- Prototyping to Production: A strong relationship between PCB designers, manufacturers, and contract assemblers ensures smooth transitions, fewer revisions, and faster time-to-market.
- Epec’s Free DFM Services: Leveraging Epec's complimentary Design for Manufacturability (DFM) services provides early troubleshooting, helping to streamline production and avoid costly design revisions.
- Global Support and Expertise: Epec offers domestic and offshore capabilities, ITAR support, and specialty engineering teams to assist in PCB design, layout, and routing for high-quality, scalable production.
