Analysis and solution of conventional solder paste reflow soldering voids 01
From: Author:Mark Hardy Publish time:2021-09-09 18:15 Clicks:0
Solder paste reflow soldering is one of the assembly processes in semiconductor packaging. Soldering voids in a larger soldering area are one of the most common and difficult to solve problems. Through the analysis of solder paste printing reflow soldering process characteristics and correlation tests, the main influencing factors that cause voids are sorted out, and the design of experiment (DOE) is used to optimize process parameters and reduce soldering voids. In order to meet the requirements of die soldering voids, a new secondary printing reflow process is adopted to reduce the die soldering void area rate to less than 5%, which solves the problem of chip cracks caused by voids, which is the soldering void problem of the conventional low-cost solder paste reflow soldering process Improvement provides a reference.
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In the circuit board assembly, solder paste is printed on the pads of the circuit board first, then various electronic components are mounted, and finally passed through a reflow furnace. After the solder balls in the solder paste are melted, the various electronic components and the circuit board are soldered. The plates are welded together to realize the assembly of the electronic module. This surface mount technology (SMT) is increasingly used in high-density packaging products, such as system in package (SiP) often soldered ball griarray (referred to as ball griarray). BGA) devices, power bare chips, quad flat no-lead (QFN) devices. Due to the characteristics of the solder paste soldering process and materials, after reflow soldering of these large soldering surface devices, voids will appear in the soldering area[1]. The voids will affect the electrical, thermal and mechanical properties of the product, and even lead to product failure[1] 2-4] Therefore, improving and solving solder paste reflow soldering voids has become a process technology problem that must be resolved. Some researchers have analyzed and studied the causes of BGA solder ball soldering voids, and provided improved solutions [5- 6], the conventional solder paste reflow soldering process has a QFN with a soldering area larger than 10 mm2 or a bare chip solution with a soldering area larger than 6 mm2.
Preform soldering and vacuum reflow furnace soldering are used to improve soldering voids. Prefabricated soldering pads need special equipment to apply flux. For example, directly mount the chip on the prefabricated soldering pad. After reflow, the chip is shifted and tilted seriously; if the chip is reflowed first, then the flux is applied to mount the chip. Two reflows increase the process. Prefabricated soldering And the cost of flux materials is much higher than that of solder paste. Vacuum reflow equipment is relatively expensive, the vacuum capacity of an independent vacuum chamber is very low, and the cost performance is not high. In addition, the problem of tin splashing is serious, and the application of high-density, small-pitch products is an important factor that restricts its application. This article is based on the conventional solder paste reflow soldering process and develops and introduces a new secondary reflow process to improve soldering voids and solve the problems of bonding and plastic packaging cracks caused by soldering voids.
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