Seventy-five to eighty-five percent of the defects in SMT chip processing are caused by solder paste defects, so solder paste defects are very troublesome in the daily production detail control process. The control details should be from the initial BOM and Gerber data sorting, to the procurement channel management of components, solder paste storage and access control, solder paste printing, SPI solder paste inspection, reflow soldering, etc.
Therefore, in the process of SMT processing, we can also strictly implement the requirements of some quality management systems to avoid or reduce the occurrence of solder paste defects. To give a simple example, in the patch processing of automotive electronics, if we can implement the quality requirements for electrostatic control, component preservation, solder paste storage and use, we can avoid the electrostatic breakdown of BGA and IC chips’ quality issues.
In addition, because the same batch of products may have thousands of pieces and tens of thousands of pieces in PCBA processing, the chip processing cycle is relatively long, and there may be dry solder paste on the stencil stencil, or the template opening and the circuit board are not aligned. Such details can lead to unwanted solder paste on the bottom of the stencil or even during processing of the PCBA foundry, resulting in poor soldering.
Here is a brief introduction to how to avoid solder paste defects in SMT chip processing.
The printing cycle is fixed in a specific mode during the printing process of the fully automatic printing machine. Make sure the stencil is on the pad, this will ensure a clean solder paste printing process. For fine stencils, if damage occurs between thin pins due to bending of the stencil cross section, it may cause printing defects and short circuits.
After printing solder paste in SMT packages, the longer an operator waits after finding a printing error, the more difficult it is to remove the solder paste. Immediately when a problem is identified, the improperly printed board should be placed in an immersion solvent, as the solder paste is easily removed before it dries.
To prevent solder paste and other contaminants from remaining on the surface of the board, wipe with a clean cloth. After soaking, scrub with a mild spray and preferably dry with a hot air blower. If using a horizontal stencil cleaner, the clean side should be down so that the solder paste will come off the board.
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