The Mannifest: Common Machine Errors and How to Avoid Them

When it comes to the quality of SMT boards you produce, it can be difficult to know where to begin and what features various PCBA machines offer are most important. To avoid common errors that could compromise the boards you’re looking to produce, be sure to keep an eye out on these key features before assembling your line.

The first thing to keep in mind when putting together your SMT assembly area is that every step of the process is equally important. Printing, placing, and reflow are all essential stages that need to be considered with equal amounts of care and attention.
Consider how involved the stencil printing process will be for your boards. While simpler board configurations can easily get by with manual or semi-automatic printing processes, more complex boards that use 01005 chips,micro BGAs, or fine-pitch components should make use of a printer with vision alignment, programmable squeegee pressure, and programmable squeegee speed. This will ensure consistent results and minimize the possibility of error that could occur during the printing process. Without these features, you run the risk of costly defects, such as bridging or insufficient or excessive solder.
When choosing your pick-and-place machine, accuracy is your key concern. You should make certain your pick-and-place has the capability to position parts with no component more than 25% off the pad before the reflow process. This is only a minimum requirement, of course, and an even high degree of accuracy is preferable. For the reflow process itself, you should ensure that the oven has the capability to run separate unique profiles per board. Today, ovens are available with predictive profiling features that can cut down on guessing and testing, and many profiling software options have become better at providing you with an accurate, workable profile on the first try.
One option you may want to consider is automating your hand soldering process by use of selective solders or wave soldering machines. Wave solder machines are generally considered a better option for single-sided boards; otherwise, pallets or masking will be required unless you’ve decided to use glue or adhesive to hold down resistors and chips to solder them on the wave. With wave soldering, you’ll experience a more consistent solder joint than hand soldering. Selective solders, on the other hand, are a great choice for complex double-sided board configurations and eliminating hand soldering in general.
While it’s important to take care when assembling your SMT line, errors in the assembly process are nearly impossible to 100% eliminate. This is where an inspection station and functional testing can come in handy. An automatic optical inspection (AOI) option can allow you to identify possible issues with your board as they occur. This also means that you’ll be aware of possible complications in your line before they become even more of an issue by making their way into the field or compromising multiple boards, multiplying the cost of repairs.
Should the use of an AOI or functional test detect any defects in your boards, a rework station can make remedying those defects go smoothly. Any rework station that simulates a reflow oven and has automatic removal and placement capabilities eliminates any problems related to operators hand-removing parts, lifting pads, and possibly causing damage to boards.
There are a number of factors to consider when beginning in-house SMT production, no matter the application of your boards. Taking care to make the right choice for accomplishing each step in the process at the outset can save you a number of headaches down the road. Whatever the final implementation of your boards, you want to make certain  that your assembly process is as accurate as possible.
This column originally appeared in the July 2019 issue of SMT007 Magazine.


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