We recently focused on the need for companies in or looking to enter the Internet of Things space to find the right printed circuit board manufacturers to speed up research and development efforts without sacrificing quality. At the same time, we emphasized the advantages that partnering with these businesses offers. By closely following the design guidelines and meeting all requirements for detailed drawings, companies can avoid revisions and delays, and fully benefit from quickturn PCB fabrication.
With that in mind, let's take a close look at seven drawing requirements in flex PCB design.
1. The Basics
First and foremost, there are several board elements that must be included in your design. These include:
- Layer count
- Finished board thickness
- PCB materials used
- Surface finish
These may seem like obvious requirements, but they occasionally go overlooked. When that happens, the PCB manufacturer will need to follow up for clarification, delaying turnaround time.
2. A Drill Symbol Chart
The drill symbol chart indicates all of the finished hole sizes, as well as the hole size tolerance, for your circuit board design. The standard finished hole size is +/- .003," but this is never assumed, so this measurement must be stated on your design drawing.
"The dimensional drawing should define the rigid to flex interfaces."
3. Dimensional Drawing
The dimensional drawing identifies a number of critical measurements for the PCB design. Notably, the dimensional drawing should define the rigid to flex interfaces, noting where these two types of material meet. While the typical outline tolerance is +/- .010", it is imperative for the designer to determine and clearly state whether this meets their specific needs. If a pallet or array is needed for the design, a dimensional view is also required.
4. Board Construction and Layer Order
This documentation differentiates between layers comprised of rigid material and layers containing flexible material, such as copper weights. Without these drawings, the PCB manufacturer will need to follow up with the customer, delaying turnaround time.
Along with the flex PCB drawings themselves, you'll need to present accompanying notes when submitting your circuit board design. These notes should encompass a broad range of specific details. For example, your notes should state:
- Class, wiring type, and installation use requirements
- Electrical test requirements
- Packaging and shipping needs
The notes should also include specific design requirements, but that point deserves its own section.
6. Specific Design Requirements
In many cases, particularly when it comes to prototypes in areas like the Internet of Things, you'll have unique PCB design requirements that do not fit into any of the above categories. In order to maximize quickturn benefits, these need to be presented as part of the design drawings early in the design process. Communication between designers and fabrication houses before designing begins and throughout the manufacturing process will speed the process even more, allowing for no confusion or delays.
This last drawing requirement isn't what you think. We're not focused on the flexibility of the PCB, but rather the design itself.
Writing for Engineering.com, Kagan Pittman noted that it impossible for engineers and designers to accurately predict all of the potential ways that a circuit board design could go awry.
Sometimes, designers will refuse to alter their designs, even when the PCB fabrication partner offers manufacturability or reliability suggestions. Industry expert Al Wright told Pittman about one such instance he ran into where the client, instead of adapting, went to another manufacturer. As a result, the PCB produced was completely faulty. If you're not sure whether the suggestions made will be applicable to your design, ask the fab house to elaborate on the potential issue.
The purpose of these drawing requirements is to help you make the most of your partnership with a PCB manufacturer. If you've chosen an industry-leading PCB firm to work with, then you should absolutely take advantage of the expertise and guidance they offer. That means you need to be flexible and open to suggestions.
For an even more in-depth look at drawing requirements, check out our Flex PCB Design Guide.