Whether you are sewing clothes, cooking food, or building circuit boards, you are going to go through a trial phase that will eventually lead to the final result. A tailor will try a partially completed outfit on its recipient to check its fit before the sewing is finished, and who hasn’t been asked by their grandmother if the stew cooking on the stove needed more salt? It is the same when we have our circuit boards built by a contract manufacturer (CM). Before we commit to having a regular production run of the boards built, we will get a prototype of the board to test and evaluate first.
Prototyping is critical to the success of PCB design. Design engineers need to get hardware into their hands quickly in order to test and debug their designs, or to try design alternatives to improve the performance of the board. Prototyping differs quite a bit from regular high-volume production runs of the same board which is focused on the need to reliably produce a large amount of boards without any defects. Let’s take a moment to examine these differences in closer detail, and see how designers and manufacturers can better work together to improve the PCB prototype and assembly process.
Understanding PCB Prototype and Assembly
Although both PCB prototyping and regular high-volume production runs will both result in an assembled printed circuit board, there are some differences between the two processes. Where a regular production run is a fixed process to ensure the reliable manufacturing of a large batch of circuit boards, the goal of producing a PCB prototype is flexibility in order for a small number of boards to be assembled quickly. This way the design engineers can begin their processes of test and debug, as well as looking for ways to improve the performance and quality of the design as soon as possible.
Flexibility is the key to the PCB prototyping process. Prototype boards are usually a work in process, and the production process must be nimble enough to allow for modifications to the board in order to accommodate design changes as they come in. Here are some examples of how prototype manufacturers will stay flexible:
- Using leaded soldering processes instead of specific non-leaded soldering chemistry for restriction of hazardous substances (RoHS) compliancy. Although the boards will need to be RoHS compliant when they are in regular production, this isn’t a requirement for the prototype.
- Not all of the components need to be included in the assembly depending on the needs and purpose of the prototype. Instead of the fine-pitch components that will be used for regular production, wider parts can be used to help with test and debug.
- Prototype boards can also include specific options for test and debug that production boards wouldn’t need. These could include additional connectors, sockets for IC’s, and test probe posts.
- PCB documentation will be changing as the needs of the prototype change; however, for minor changes or adjustments full documentation may not be necessary. This is especially true for assembly as some changes do not require change orders. For example, modifications that will be reset for the final prototype.
Another way that CMs can be flexible with their prototype builds is to relax their design while remaining within manufacturability standards. Although these are a must for regular production runs, many DFM issues can be corrected through a manual assembly and rework processes. Again, the whole goal is to get the prototype board build quickly and back into the hands of the design engineer. Assembling PCBs for a regular high-volume run is very different though.
High-Volume PCB Assembly
Where flexibility is the name of the game in order to get a PCB prototype quickly assembled, a regular high-volume run of PCB manufacturing relies on a fixed process to deliver the most consistent results. The goal here is the distribution of high-quality circuit boards without any assembly errors in order to keep the manufacturing process flowing. To do this requires the opposite of what a prototype build does:
- The PCBs must be built to all required industry standards, and their design must be optimized in order to meet RoHS and other compliance-related regulations.
- The boards must be fully assembled, and any part substitutions that the prototype version used for test and debug must be reconfigured with regular production level components.
- All DFM requirements must be included in the production design. This includes design for assembly and design for test rules in order to achieve maximum manufacturing yields.
- All documentation requirements need to be fully met in order to satisfy any industry safety and standards testing that may be required.
Working with Your CM on Your PCB Manufacturing
As described above, there are design modifications that can be used to speed the assembly of your boards during prototyping. These are summarized below.
|PCB Prototype and Assembly Modifications|
|Flexibility over fixed processes|
|Boards may not be fully assembled|
|Different parts may be substituted for test|
|Options for test and debug such as sockets|
|DFM tolerances can be relaxed within standard|
|Documentation may not change with the board|
To ensure that the manufacturing of your PCB goes as smoothly as possible, there are some things that you can do to help. To start with, enlist the services of your CM as early on in the design cycle as possible. They’ve been doing this for a long time and have a lot of skill and experience in setting up a board for the best possible manufacturing results. For instance, your CM will have a lot of valuable information that will help you in choosing the correct materials and board layer stackup for your design. Another thing that you can do is to follow their engineering recommendations on your design so that from the very start you are working towards a production level design. This will reduce the amount of DFM changes that you will have to make when your design transitions from the prototyping phase to regular high-volume production.
|Tempo‘s Custom PCB Manufacturing Service|
At Tempo Automation, we are ready to work together with you on your prototype and/or high-volume PCB manufacturing. We have the experience and the resources that you need to make sure that your design is manufactured to highest levels of quality.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on CAD files or how to incorporate your design into a CAD format, contact us.