PCB (printed circuit board) heat-radiation soldering pad used for QFN (quad flat no-lead package) chip, and QFN chip and PCB soldering method

Abstract

The invention discloses a PCB (printed circuit board) heat-radiation soldering pad used for a QFN (quad flat no-lead package) chip. The PCB heat-radiation soldering pad is provided with heat radiation via holes not larger than 0.3 mm in diameter and escape holes 0.8-1.2 mm in diameter. The invention further discloses a soldering method adopting the heat-radiation soldering pad. The soldering method includes printing ink used for plugging the heat radiation via holes on one side of a PCB which does not need soldering in correspondence to the heat-radiation soldering pad; painting tin paste on the heat-radiation soldering pad by a mesh plate without holes corresponding to the escape holes; attaching the QFN chip to the corresponding position of the PCB, so as to enable the QFN chip to expose to be flush with the PCB heat-radiation soldering pad and a pin area of the QFN chip with a PCB pin soldering pad; soldering the QFN chip on the PCB by reflow soldering. By the method, gas escape can be helped in the soldering process via the escape holes, soldering tin outflow can be prevented and good soldering effect is achieved.

Description

technical field [0001] The invention relates to printed circuit board welding, in particular to a PCB heat dissipation pad used for QFN packaged chips and a method for welding QFN chips and PCBs. Background technique [0002] QFN (Quad Flat No-lead Package) is a high power density package. figure 1 is a schematic cross-sectional view of the QFN package structure, figure 2 is the bottom view of the QFN chip. refer to figure 1 and figure 2 , Chip 1 is placed on exposed pad (exposed pad) 2 . The functional terminal on the chip 1 is electrically connected to the lead area 4 arranged around the exposed pad 2 through the wire 3 . Finally, the chip 1 is wrapped and packaged by the package body 5 . Wherein the exposed pad 2 and the lead area 4 are both exposed on one side of the package body 5 . [0003] When the QFN chip is mounted on the PCB, it is welded on the PCB in a bonded form. The pin area 4 of the QFN chip corresponds to the pad at the corresponding position on t...

AI Technical Summary

Problems solved by technology

However, when mounting QFN devices, in order to ensure the quality of soldering, the via holes opened on the heat dissipation pad are usually blocked with ink on the side that does not need to be soldered (that is, the back of the PCB). The purpose is to prevent the heat dissipation pad from When the solder on the heat sink passes through the furnace, the solder on the heat dissipation pad will flow to the non-soldering surface through the via hole, resulting in a decrease in the amount of solder on the soldering surface. If the amount of solder is reduced, it will lead to poor soldering; If it is blocked, it will not be able to play the role of the original auxiliary gas escape

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