MLCC in the LED driver circuit

MLCC are called multi-layer (laminate, laminated) chip ceramic capacitors. The acronym is MLCC. The MLCC easily cracks from the solder joint when exposed to temperature shocks. At this point, the small-sized capacitor is better than the large-sized capacitor. The reason is that the large-capacity capacitor does not reach the entire capacitor so quickly. Therefore, the temperature difference between different points of the capacitor body is large, so the expansion is different. stress. In addition, the expansion coefficient of the MLCC and the PCB in the cooling process after MLCC welding is different from the stress-induced cracking. To avoid this problem, a good soldering temperature profile is needed for reflow soldering. If wave soldering is not used for reflow soldering, then this failure will be greatly increased. MLCC is to avoid the manual soldering process with soldering iron. However, things are not always ideal. Soldering iron soldering is sometimes unavoidable.

It is well known that the IC chip is packaged and dual-inline. It is generally believed that the difference between the patch type and the dual inline type is mainly that the volume is different and the welding method has a different effect on the system performance. In fact, there is an antenna effect on every trace on the PCB. Each component on the PCB also has an antenna effect. The more conductive part of the component, the stronger the antenna effect. Therefore, antenna effects that are smaller than the package size for the same model chip package size are weak.

It is easier for the same device to use a patch device than a dual-line device to pass the EMC test. In addition, the antenna effect is also related to the operating current loop of each chip. To weaken the antenna effect In addition to reducing the package size, the operating current loop size, operating frequency, and di/dt should also be minimized. Paying attention to the pin layout of the latest models of IC chips (especially monolithic chips) will find that: Most of them have abandoned the traditional way - in the lower left corner is GND in the upper right corner is VCC / and VCC and GND are arranged in adjacent positions in order to reduce Operating current loop size.

Not only IC chips, resistors, capacitors (BUZ60) packages are also related to EMC. With a 0805 package with better EMC performance than 1206, with a 0603 package and better EMC performance than 0805. ' The current international fashion is the 0603 package ' part package, which refers to the appearance and location of the actual parts when welded to the circuit board. is a purely spatial concept so that different components can be shared with the 10 package ' same components can also have different parts of the package. Like resistors have a traditional pin resistor ' This component is large in size, the circuit board must be drilled to be able to place the component, complete the drilling after inserting the element again over the tin furnace or spraying tin (also proceed welding) the higher cost/newer design is the use of small surface SMD components (SMD) This component does not have to drill, With the steel film will be half molten solder paste into the circuit board and then put the SMD components on, you can weld on the circuit board.