Understanding 3D Solder Paste Inspection

What Is the Importance of Solder Paste Inspection?

Solder connects components to the printed circuit board. The performance of the electronics depends on the quality of these connections. Nearly all solder joint defects are due to improper solder paste printing. Solder paste inspection can dramatically reduce the defect rate.

How Can Solder Paste Be Inspected?

Solder paste inspection or SPI can be done by dedicated SPI systems as well as by trained human QC technicians. Automated inspection could involve 2D inspection via X-rays and cameras. 2D pictures can verify the alignment of the solder paste on the board. Angle cameras can take 3D pictures that verify both the alignment and volume of the solder paste. This improves both the print quality and the yield of your soldering processes. Whether or not you get accurate measurement of solder paste placement and height will depend on the method used, though automated systems are almost always more accurate than human verification, especially at high speed.

What Are the Benefits of 3D Solder Paste Inspection?

3D inspection is designed to verify both the height and footprint of solder paste targets before you insert the parts to be soldered into place. The data from 3D solder paste inspection may allow for part placement that compensates for warpage.

Or you may have the solder paste repaired or redone rather than having a defective solder joint. Repairing the solder joint after part placement is more difficult and time consuming and therefore more expensive. For example, 3D solder page will identify when the solder paste has formed a droplet or pyramidal shape. It covers the bottom of the board, but it will not sufficiently cover the wire coming off of the component. Manual touch-up of solder requires skilled labor, and sending these PCB for rework interrupts the flow of the assembly line. This is why it costs about ten times as much to rework defects

Automated solder paste inspection can often run at the same speed as your assembly line. Even if it is slower, it will be far faster than human quality control inspections. Nor do you have to worry about variations in the quality of inspection due to differences in opinion or sloppy work from tired inspectors.

Automated solder paste inspection automatically collects data for later reference. You will know which boards have voids or variations. You can generate reports that show the actual defect rate and the breakdown of the types of defects. In contrast, manual inspection may not catch every defect, and the human operators may not document every issue when they send something on for rework. 3D SPI allows you to see the progression of a problem over time, tracking it back to the origin point and allowing you to eliminate the root cause.

Furthermore, you can use automated inspection to inspect completed rework of solder joints and component placement after the solder has been reflowed. You’ll verify the quality of the solder joints before the assembled printed circuit boards are inserted in the final product or packaged for shipment. Overall quality levels go up, and your customers will appreciate the more reliable product they get from your company. You aren’t relying on statistical sampling and risking a few defective items reaching your customers.

Automated inspection means you have tighter process control. You can see when there are dangerous trends in various metrics before it hits the rejection threshold. You can address problems before you get multiple rejections. This results in higher quality and improved yields, especially in products where rework is difficult or not cost-effective.

Solder paste inspection processes can reduce your scrap rate. Depending on the types of errors you see, it may help you save money on material, as well. For example, you can optimize the amount of solder paste applied to the boards, eventually reducing the amount required while maintaining the performance of your final product. Furthermore, you might see a reduction in certain types of errors if you aren’t using more paste than necessary.

What Are the Issues with 3D Solder Paste Inspection?

Solder paste inspection machines are a capital expense that some are reluctant to make. You need to make space on the assembly line to install them. That requires time, money, and planning. All of this requires making an up-front investment that causes some to delay or avoid adopting 3D solder paste inspection despite the potential cost-savings. Others have heard about the mediocre quality of older solder paste inspection machines or think it isn’t an option in their case. However, the newest generation of three dimensional solder paste inspection machines has a smaller footprint and far greater accuracy than their predecessors. Better yet, training a solder paste inspection system will be faster than training a steady stream of human inspectors.

How Can You Get the Most Out of SPI Systems?

Advances in artificial intelligence mean that solder paste inspection or SPI systems can be trained to recognize what a proper solder paste profile looks like for your specific product. If you buy a system, it may be programmed to check your solder paste lots based on predefined criteria. Or you could train it to use your in-house criteria. In this case, you’d have it scan multiple examples of “perfect” solder paste. Then it knows what metrics to use, even if it has to extrapolate the definition of good enough solder paste applications.

Automated 3D solder paste inspection could be an automated optical inspection or AOI, X-ray, or combination thereof. Three dimensional optical inspection will by definition catch more defects than two dimensional such as when the solder is inconsistent. For example, gaps in the vertical column become evident in three dimensions when it might be missed in an optical 2D inspection. Yet it is X-rays that see voids in the solder paste. A combination of inspection methods before and after the solder reflow process will capture complex defects which can be caught by slow, expensive human inspectors, too. This is why a combination of inspection technologies yields the greatest results.

High speed PCB assembly processes dramatically increase throughput and profits. Yet you need inspection systems that can keep up with the production line and your customer’s ever higher expectations if you want to stay in business. If you would like to learn more about the 3D Solder paste inspection process or other circuit board process, reach out to the professionals at Geospace Technologies.