The full name of the chip capacitor is called a multilayer (stacked, laminated) chip ceramic capacitor, abbreviated as MLCC. When the MLCC is subjected to a temperature shock, cracks easily occur from the welded end. At this point, the small size capacitor is relatively better than the large size capacitor. The principle is that the large size capacitor does not reach the entire capacitor so quickly, so the temperature difference between the different points of the capacitor body is large, so the expansion is different. Stress is generated. This is the same as thick glass when it is poured into boiling water. In addition, during the cooling process after the MLCC is welded, the expansion coefficients of the MLCC and the PCB are different, so that stress is generated and cracks are caused. To avoid this problem, a good soldering temperature curve is required for reflow soldering. If wave soldering is used without reflow soldering, this failure will increase significantly. MLCC is to avoid the process of soldering with a soldering iron. However, things are always less than ideal. Manual soldering of soldering irons is sometimes inevitable. For example, for electronic manufacturers of PCB out-of-process processing, some products are extremely small, and manufacturers who are not willing to pick up such a single chip can only be soldered by hand; when the sample is produced, it is usually hand-welded; When repair welding, it must be hand soldered; when the repairman repairs the capacitor, it is also hand soldered. When it is unavoidable to manually weld MLCC, it is necessary to attach great importance to the welding process.
As is well known, the IC chip is packaged in a patch type and a dual in-line type. It is generally believed that the difference between patch type and dual in-line type is mainly different in volume and welding method, and has little effect on system performance. actually not. There is an antenna effect on every trace on the PCB. There is also an antenna effect for each component on the PCB. The larger the conductive portion of the component, the stronger the antenna effect. Therefore, the same type of chip has a smaller package size than the larger package size.
In the same device, it is easier to pass the EMC test using the chip component than the dual in-line component. In addition, the antenna effect is related to the operating current loop of each chip. To reduce the antenna effect, in addition to reducing the package size, the operating current loop size should be minimized, the operating frequency and di/dt should be reduced. Pay attention to the pin layout of the latest IC chips (especially monolithic) and find that they mostly abandon the traditional way - the lower left corner is VCC in the upper right corner of GND, and VCC and GND are arranged in adjacent positions, just to reduce Small operating current loop size.
Not only IC chips, but also resistors and capacitors (BUZ60) are also related to EMC. The 0805 package has better EMC performance than the 1206 package, and the 0603 package has better EMC performance than the 0805 package. Currently popular in the world is the 0603 package. Part packaging refers to the appearance and solder joint location indicated when the actual part is soldered to the board. It is a pure space concept. Therefore, different components can share the same component package, and the same component can also have different component packages. Like the resistor, there is a traditional pin-inserted type. This kind of component is bulky. The circuit board must be drilled to place the component. After drilling, insert the component, and then pass the tin furnace or spray tin (also hand soldering). High, newer designs use small-size surface-mount components (SMD) that do not require drilling. Pour the semi-molten solder paste into the board with a steel film and place the SMD component on it. Soldered on the board.
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