When you handle your SMT work in-house, it's up to you to navigate any complications you may have with the design process. One of the best ways to eliminate possible production issues is to ensure that you have a manufacturable design. Thus, there are several factors to keep in mind when reviewing your designs before bringing your production in-house or starting your first run of in-house prototypes.
One of the first things to consider when bringing your production in-house is the maximum size of your boards. Ensure that the machines you're looking into can accommodate the design that you have in mind, or be ready to adapt that design if you find that to be the more cost-effective option. Most manufacturers recommend at least 3 mm of edge clearance, so be certain to consider that when working on your boards' layout. Consider using edge rails on the boards if your components are up to or close to the edge of the boards. Taking care of anticipated issues in the initial steps of the design process can save you from headaches down the line.
When designing double-sided boards, include fiducial marks on both sides of your board. These markers will give your machines' imaging systems a point of reference to work off of when assembling your boards ensuring accurate placements for fewer defects. For the best results, stick to the standard round fiducials of 1–1.3 mm and try to keep away from any marks or via holes on the board that look similar. It's also best to keep these marks on the opposite corners of your board, diagonal from one another, for the highest degree of accuracy.
If you're designing a mixed technology board using through-hole parts and SMT, it's best to keep the SMT on a single side of the board and to have the through-hole parts protrude through the bottom of the board to allow for wave or dip soldering. If you're running a double-sided design, keep in mind you will have to solder the through-hole parts with a selective solder, hand solder them, or get specialized pallets to run that assembly through a wave solder machine. Double-sided boards offer some other challenges, many of which were addressed in my last column, but a key part of double-sided design is ensuring that lighter components are on the bottom of the board during the double-sided reflow process.
The size and shape of your board itself can also have an impact on how your boards are transported through the SMT process. If your board is round or odd shaped, it can be difficult to plan out exactly how it will travel through your SMT line. Find a way to ensure that the edges of your board are square for ease of transport through the SMT line. If not, you'll need to find a solution, such as incorporating fixturing pallets for the board to be processed through the SMT line, or a removable frame portion in your design to be depanelized later.
If your final product is small boards, you may want to consider panelization of the boards as an option to increase your production throughput and minimize handling. Provided that you optimize your placement order, this process can cut down on your pick-and-place time, organizing all parts of a type to be placed one after another across multiple boards to cut down on the number of nozzle changes. In addition to those benefits, panelization is also great for freeing up operator time for other tasks as they can dedicate less time removing individual finished boards and reloading the line itself.
It may seem obvious that design is the first step in producing a quality SMT product, but it’s essential to get your production started on the right foot, especially if you're transitioning to in-house PCBA work. Rather than being the concern of an outside contractor, issues and challenges with your design become your own and can become overwhelming quickly. Taking the time to ensure that you have a workable, stable design upfront can alleviate a world of stress in the long run.
Mike Fiorilla is a writer at Manncorp Inc.
This article was originally published in the June 2019 issue of SMT007 Magazine.