SMT (Surface Mount Technology) Assembly isn’t a zero-defect soldering process. Even superficial defects can cause your PCB to fail, so minimising or avoiding them at all costs is the only solution.
In order to achieve the highest product quality, it’s crucial to gain a thorough understanding of the common defects encountered. But before that, let’s take a quick look at what the SMT process is all about.
Defining Surface Mount Technology
SMT is a much sought-after and broadly used component assembly technique in the PCB manufacturing sector. SMT or Surface Mount Technology helps mount all the electrical components directly onto the PCB. It has several advantages over through-hole mounting, allowing automation, high component density, efficient space utilisation, and greater circuit speeds for superior board performance. The process is also cost-effective and provides higher stability. The telecom, aerospace, and automotive industries are just a few that benefit from SMT assembly
Troubleshooting SMT Assembly Defects
From installation to soldering, the assembly experts ensure the substrate is in a zero-defect condition. However, it’s difficult to avoid errors entirely. Knowing what is causing what is the first step to making sure you can eliminate defects as much as possible. So, here are three common problems assemblers might encounter:
Defect #1. Open Solder Joints
This one’s impossible to detect many times unless you’re using a magnifier or AOI (Automatic Optical Inspection machine) , you won’t be able to confirm and fix vertical gaps between the component lead and PCB pad. There could also be asymmetric pads, improper aspect ratio, solder paste/ component lead/ PCB pad contamination, open vias, or incorrect reflow. But, there are a few ways to mend this defect, including stencil or PCB design changes, improved material handling, better reflow profile, and enhanced solder paste handling
Defect #2. Component Misalignment
The board can have IC pins misaligned, components misaligned in the same direction, random unevenness, excess solder, smaller components positioned closer to larger ones, etc. Therefore, a visual inspection is indispensable for identifying issues with the component arrangement during the assembly process. To fix erroneous placements, check for bent pins, component arrangement, stencil registration, excessive vibration, and paste deposition.
Defect #3. Solder Shorts
Solder shorts, also called bridging, arise when molten solder connects one lead to another. This kind of crossing can lead to serious performance malfunction when the board may be powered up for electrical testing. Some of the most widely recognised reasons for bridging include too much solder paste deposition, solder paste cold stump, improper reflow profile, and placement inaccuracy. To fix the error, change the stencil or PCB design, improve stencil printing, or enhance the mask printing process.
Measures To Improve SMT Assembly Process
There can be multiple causes affecting the SMT assembly process. However, some standard measures help keep the process as superior and error-free as possible.
- Ensure solder paste quality along with rigorous management of environmental humidity and temperature
- Place stencils according to the markers
- Maintain optimal speed of scrapers for correct placement of solder on pads
- Stick components correctly to the corresponding positions
- Ensure fast pick and place for chip mounting
- Take care of the component selection and mounting position and pressure
- Have an appropriate design for the stencil, pad, thickness, etc.
- Follow this path to set the temperature curve right: Soldering > Preheating > Temperature Rising > Reflow > Cooling.
These and many more measures apply to ensure the board’s quality and performance aren’t compromised. If it seems all too overwhelming, outsource your project to local experts to maintain the dependability of your product.
Need Technical Assistance? Contact ATMWA.
At ATMWA, quality and on-time deliveries are of utmost importance to us. Our knowledgeable operations can support quickturn prototypes to full production runs at our state-of-the-art facility. Our SMT assembly lines are ISO 9001 certified, exceptional quality print circuit boards, utilising the best in class processes. If that’s something you want, contact us today to discuss you PCB project
