When it comes to printed circuit board assembly and SMT equipment, the question isn't if you will have quality issues from time to time, but when. The key to keeping the "when" to a minimum is to start with good equipment, have a reliable source of advice on hand, and know where to begin when these issues pop up.
At Capital Equipment Exchange, we've put together information to help you spot and troubleshoot some of the most common causes of SMT problems or PCB defects.
Solder balls are pretty easy to spot. You have solder balls if you see lots of tiny balls just outside the flux residue areas. If these balls are appearing alongside your PCB components, you have beading.
Start with your stencils. Solder paste can get smeared underneath your stencil. Stencil cleaner may be getting left behind. You may have a stencil thickness or squeegee pressure problem. Stencil alignment also plays a role in keeping your boards ball and bead free.
Sometimes you'll start to have solder paste running between component contacts. If left unchecked, you have a quick recipe for short circuits in progress. A batch of short-circuiting PCBs should be checked for bridging problems.
Like troubleshooting for balls and beads, you'll want to ensure your squeegee pressure, stencil thickness, and alignment aren't off. If everything looks good there, pay attention to your paste viscosity, screen print speeds and temperatures, and reflow ramp-up times.
Sometimes no solder, or not enough solder, will be placed. This can lead to an open circuit or insufficient solder on the joint between a component lead and pad.
These solutions are going to start sounding familiar. It makes sense if you think about how many issues result from improper solder application.
If you are starting to notice specific components standing upright on one end, you have yourself a case of PCB tombstoning. Usually, you'll have passive components, like resistors or capacitors lifting from the board, creating an open circuit, and ruining your PCBs.
Smaller components, higher temperatures, and lead-free solders can contribute to tombstoning problems.
When you start troubleshooting a component tombstoning problem, you'll want to start with the pad. Is your component pad the right size?
You set up your equipment to place solder paste in a specific area and expect it to stay there. Unfortunately, your paste will tend to spread or slump. This can lead to bridging and short circuits. So, whether you're dealing with hot slump or cold slump, you'll want to nip this issue in the bud ASAP.
While hot slump is most likely happening as your paste gets warm during preheating, cold slump can happen for various reasons: temperature, paste viscosity, drying times, and the height of the deposit.
With dewetted solder joints, you will notice good component lead and pad contact but no bonding between the solder and pad. Your first clue that dewetting is occurring might be intermittent connections. Dewetting is usually caused by PCB contamination.
If orange skinning is your problem, you will start to notice the texture of your solder joints looking dull, rough, and well, like an orange peel. PCB orange skinning issues are usually temperature-related.
If, as you troubleshoot, you realize your PCB machines are the problem, buying new isn't your only option. Save time and money with used SMT equipment from Capital Equipment Exchange. We not only stick around after your purchase for any issues that arise, but we can help you find spare parts to extend the life of your existing machines as well. Contact us today to get the latest on our inventory or find out more about our streamlined purchasing process.