If you are a weekend “handyman” like I am, jumping into a household repair project is a lot of fun. Managing a large project, however, can still be intimidating. I learned that last year when I started building a new backyard shed. With only a simple set of instructions and many piles of building materials in front of me, it was a bit daunting. In the end, though, the shed came out great, and I’ve received a lot of compliments on it. The key to success, I found, was making sure that I was prepared by asking the right questions up front so that I could make the right decisions.
Looking for a contract manufacturer to build a large PCB prototype board is actually a very similar scenario. It can be overwhelming to consider all of what needs to be done to get your board built on time and within budget. The way to be successful here is to also ask the right questions up front. This way, you will be able to choose the right CM for your project and make sure that your prototype board is built correctly. Here are some of the key points in manufacturing large PCBs that you should consider.
When Is Your Design Considered a Large PCB Prototype Board?
First of all, let’s take a look at what would be considered to be a “large” board. A circuit board that is more than 12 inches wide is considered large. When you are doing a layout that is 20 inches wide by any length, you are definitely designing a large board. At 30 inches wide, you have reached the limitations of the automated surface mount technology assembly systems. Anything wider than that and alternative manufacturing methods must be considered.
Layer count is also another consideration to keep in mind. A large board is often being used as a backplane, which typically requires a significant number of layers. Additionally, these boards will usually have a large number of connectors on them, and often include thick power and ground planes. Both of these issues can have an impact on the assembly processes.
Considerations to Be Aware of When Manufacturing Large PCBAs
Manufacturing a large PCBA can bring with it some challenges that a regular-sized PCBA wouldn’t have to contend with. Here are some of those areas that might be affected by a large board:
- Quick-turn fabrication: Not all fabrication vendors are set up for quick-turn processes. PCB technology, such as high-speed design, impedance control copper thicknesses, and the volume of copper for traces, can slow down the quick-turn fabrication of a board. These same factors can further slow down the production of the board when it is larger than industry standards.
- High-layer-count fabrication: PCB fabricators are qualified by CMs based on their fabrication capabilities for circuit board layer counts. Typical qualifications are two to four layers, six to 10 layers, and 12 and above layers. The higher the layer count, the more specialized the supplier must be, which could also slow down the fabrication of a large PCB.
- Price: PCBAs are built on panels. Since you are normally paying for the price of a panel, the more PCBs that are fabricated in a panel will lower the unit cost of each PCBA. Since large boards don’t fit on traditional panel sizes, you will be paying more per unit than for a smaller board.
- Thermal impact: The thickness and number of power and ground planes in a larger board could have a thermal impact on the soldering processes. The more metal on the board, the more heat and solder materials will be required. This could cause the solder reflow profile optimization to take longer than normal to define.
- Large number of connectors: With multiple connectors on a backplane, more effort in creating and working with the test fixture will be required. Typically, all connector pins need to be contacted by the test fixture to fully test and validate the PCB fabrication and assembly processes. With the large number of connector pins on the backplane, this can lead to longer test times.
All of these situations can be easily handled by a CM that is experienced with working with large boards. When choosing a CM to build your large prototype board for you, there are a few specific things to consider.
Choosing a CM for Your Large PCB Prototype Board
When searching for a CM to build your prototype, you need to know that the CM has the experience you need in building large circuit boards. Before committing to a CM, ask about their:
- Manufacturing processes: You should find out if the CM is able to handle issues such as the thermal impact of large boards, and whether or not they have the flexibility in their manufacturing processes to adapt to these needs.
- Testing capabilities: Another issue is the impact that multiple connectors can present for testing, and whether or not the CMs capabilities can fully test your large board.
- Fabrication vendors: The CM you choose should also have good relationships with several PCB fabrication houses that can handle different board sizes and layer counts, and especially ones that can quickly turn a large PCB like yours.
In the end, when you’re designing a large PCB prototype board, you need a CM that knows how to work through the different challenges and issues that these larger-size boards can have during manufacturing. Working with a CM with adequate experience and expertise gives your prototype the best chance for success.
