Large or small, every company wants to decrease costs without affecting the quality of their products or services. There is rarely a perfect way to achieve this and PCB design and assembly is no exception. Accurately assembling PCBs is not an easy task; it takes experience, technology and, above all, dedicated people to ensure your projects are done right. When searching for a low-volume assembly shop to populate your boards, it may be tempting to use a low-cost shop to save money. However, doing so may end up costing more in the long term due to reliability concerns and lower throughput, which could result in a damaged reputation. As the famous adage goes—you get what you pay for. With thoughtful planning, you can incorporate the following eight design principles and cost saving steps to bring the overall price down while still using a high quality shop and getting high quality results.
1. Design within Standard Specifications
By using industry standard sizes and components, the assembly team can use processes that have already been established and thoroughly tested. They will also be able to automate large portions of the process and avoid costly and time-consuming hand placement and soldering. Knowing what the assembly house is capable of is a matter of experience and research. Assembly houses should include their capabilities on their websites or provide a link in brochures which should answer most questions of what they can successfully handle. Any questions that are not answered by these sources can be directed to the company itself. The responsiveness of the company to your questions about their capabilities should be a good indicator of the type of service that you will receive if you become a customer.
When asked for capabilities, assembly houses will provide what they are capable of but not necessarily what is cost-effective. As a general rule, it’s always a good idea to not push the design limitations as much as possible. If it is possible to use larger traces, or greater spacing between components, then why not do it? It may or may not make the process easier but if it does not affect the operation of the board, then it only has the potential of helping. Also, when speaking with the assembly house, ask if there is anything specific to their process that may help bring the overall cost down. These suggestions may have a considerable impact on the design of your PCB, so it may be a good idea to start looking into assembly houses towards the beginning of the design of the board once you have a general idea of what you will need.
2. Consider the Costs of Mixed Mount Technologies
When building a board with solely surface mount technology parts, the boards typically have solder paste applied and are then populated and run through a reflow oven to complete the soldering process. Even for low volume assembly where most components are hand soldered, mixed technology requires more time and effort. Depending on the disparity of sizes between through-hole and surface-mount components, different soldering iron tips, temperatures, and solders may need to be used. If this low volume assembly is a pre-cursor to larger volume and more automated assembly, the difference in complexity becomes even more pronounced and is a larger concern. In the case of through-hole components during high volume assembly, when they are placed on the board they are then wave soldered. However, when there is a combination, things become more complicated. There are three combinations of mixed technology: single sided SMT and through-hole, double sided with SMT on one side and through-hole on the other, and double-sided with both SMT and through-hole on either side. Each of these scenarios is dealt with differently, but require significantly more steps and have more stringent requirements than a single technology on the board. For example, even placing SMT and through-hole components on one side requires the additional steps of applying an adhesive to the SMT components, allowing the adhesive to cure, flipping the board and then wave soldering it. As the solder bath temperatures can destroy some SMT components, you will need to verify that the SMT components are wave solderable, making your component selection criteria even more stringent. When there is mixed technology on both sides of the board, this becomes even more complex and frequently requires hand soldering of certain components after the automated process. This is not to say that you cannot mix technologies or utilize both sides of your boards for components, merely that you should weigh the benefits and drawbacks of each and make sure that mixing the technologies is worth the additional cost and assembly time for your application.
3. Panelize your Boards
The size of panel that is acceptable depends on the assembly house, but this information can save considerable amounts of money. By using the largest panel size possible, you can drop assembly costs by eliminating pick and place downtime. For an example, assume a single sided SMT board with 200 parts and a pick and place speed of 6,000 components an hour. In this scenario, it would only take two minutes to fully populate each board once the board was fully situated. After the board is complete, it will then need to be removed and replaced with a new unpopulated board, either manually or via some form of conveyor. At best, this could take approximately 15 seconds and potentially much more. If the board needs to be moved and replaced by hand it could either take a minute or two for a worker to make the switch, or require the worker to stand there and watch the pick and place work. Both of these options require a significant amount of labor. If the process is automated and takes 15 seconds to switch out a board, over 10% of the component placement time will be in moving boards. If you are able to get 10 boards on a panel, those 15 seconds will only apply to every 10 boards, meaning only slightly over 1% of the time spent populating the board will be moving the board into position. If it takes longer than 15 seconds to switch out a board or the pick and place is faster than 6,000 components an hour, the time savings—and therefore cost savings—will be even greater. It is in your best interest to find the largest panel size your assembly house can handle, and put as many iterations of your design on that single panel as possible. It should be noted that the benefits of panelizing boards are only applicable if it is the same design repeated multiple times on a single panel. Including multiple designs on one panel will not provide any cost savings as the panel will, in essence, be a larger, more complex single board.
4. Minimize Overages
If you are producing a low volume of boards, use an assembly house that does not require reels or major parts overages. If you only need 30 boards and only one or two of each component on each board, it does not make sense to buy a reel of literally thousands of parts. At the prototyping stage, components can be changed out quite frequently in the design and you may end up with a great deal of parts that serve no purpose and may have cost considerable amounts of money. Some assembly houses can machine place parts without needing large reels or tubes of parts. While researching the company, find what each is capable of handling—if they require you to purchase large reels for small prototyping runs, look elsewhere.
While you do want to minimize the parts necessary for your build, do not forget to include a small amount of overage in your requirements calculations. Parts, particularly the incredibly small 0402 and 0201 components, can be dropped by the pick-and-place machine or damaged at some point in the process, so your assembly house should have general guidelines on how many extra parts you need to provide. Excess parts after the assembly will be shipped back with the parts.
5. Seek External Review
Whenever possible, have someone else review your work. When your circuit boards are submitted to a PCB manufacturer or assembly house, trained technicians or engineers will look at the design and verify that it is manufacturable. This is an invaluable service that has saved many designs from basic errors over the years. However, these technicians and engineers are focused on the manufacturability and do not know the purpose of the board. By asking a member of your team to review your work and provide a fresh perspective, you reduce the risk
of missing simple yet crucial errors. If you are unable to find someone with the experience to provide feedback, even explaining the board to someone who is not particularly knowledge in the field will help you to step through and verify the functionality of the design to yourself.
6. Take Advantage of First Article Service
With prototypes, even after thorough and repeated review, it is still likely that there will be concerns. With final designs, while less likely, it is still possible that there is some error that will be manifest in the end product. Many assembly houses will populate one board and send it out for review, testing, and verification before continuing on the process. If they offer this service, take advantage of it. Hopefully all is well with the board, but if not, it could save a tremendous amount of money to catch the problems before potentially expensive components are attached to boards with errors on them.
7. Order in Volume
Once you are confident with your design and do not expect many changes, it would be best to get boards manufactured and populated in as large of quantities as possible. Economies of scale is a familiar concept, but in regards to PCBs, it is even more relevant than usual. The actual materials involved in the production of the PCBs are relatively minimal and the assembly of a PCB only has the cost of solder, electricity, and maintenance for the machines who place and reflow the boards. However, the time it takes to ready designs for these steps is quite extensive. There are a multitude of steps required before the actual boards are even placed into the pick and place machine. The assembly house needs to review the provided design and clarify any confusion or discrepancy, before loading the design into the pick and place machine. The parts provided are then placed into the machine, which depending on the amount of parts, could be a long and tedious process. Even if the placing will be done by hand, the process will accelerate substantially after the first few boards as the workers become more familiar with the components and where they go.
Many of the assembly houses that perform prototyping assembly are also fully capable of providing large-scale assembly. There are many benefits of using the same assembly house for both levels of production, the largest benefit being that they are already aware of your project and requirements whereas a new assembly house would need to gain familiarity with the project requirements and the production pitfalls associated with their particular system. Ordering in volume is always a gamble as everyone in the industry has had the experience of creating large piles of very costly coasters. By using the same assembly house, you can further reduce the risks of high volume ordering as you will already be familiar with the way they work and they will be familiar with your needs. However, in the end, it is up to you and the engineers on your team to reach the level of confidence where the benefit of the cost savings is no longer outweighed by the risk of having design flaws.
8. Provide Helpful Information to the Manufacturer
If there are any special requirements or areas that you believe will cause concerns, contact the company and discuss it with them. They may be able to provide design advice that eliminates these concerns or maybe let you know that the design is unmanufacturable. Most likely, however, they will pay special attention to where you have indicated and perhaps make minor tweaks to their processes to ensure that it is done correctly. Knowing beforehand can save a lot of time and money on rework that could have been avoided.
There is rarely too much information provided when submitting boards for manufacturing and assembly. If there is information that is recommended but not required, include it when you can. For example, Advanced Assembly does not require fiducials in order to process and successfully assemble circuit boards. However, the fiducials are an additional help that could reduce the difficulties in the assembling process and could improve the final product due to increased accuracy. If it is possible to include fiducials on either the PCB or panel, do so.
It is possible to decrease costs without giving up quality. Instead of using cut-rate manufacturers and assembly houses, follow these low-to-no cost recommendations that will save you the money you need to make sure that your designs are produced to the highest quality possible. Never settle for less than the standards that you and your customers expect.