An assembly process method based on fine pitch qfn device and ceramic encapsulated qfp device

Abstract

The invention relates to the field of SMT assembly processes, and discloses an assembly process method based on a fine-pitch QFN device and a ceramic-sealed QFP device. The method comprises the following steps: pad design: setting the size of a fine-pitch QFN device pin to be larger than that of a real object, enabling the size of a ceramic-sealed QFP device printed board pad to be larger than that of the device pin in the width direction, and leaving redundant space at the root and the toe in the length direction; pretreatment of the device: dipping the abdomen part of the fine-pitch QFN device and a pin bonding pad with a soldering flux, carrying out device pin bending forming on the ceramic-sealed QFP device to realize stress release, and carrying out gold removal and tinning on the ceramic-sealed QFP device by using a tin pan; silk-screen printing: setting the size of an opening of the fine-pitch QFN device to be equal to or larger than that of a pin, and enabling the size of an opening in the abdomen to be contracted and the shape of the opening to present a 4-grid pattern or a 9-grid pattern; reflow soldering: using a vacuum welding furnace, and adopting a step vacuumizing mode in the welding process; and inspection and detection: carrying out void ratio detection and tin-climbing wetting state detection, and assembling to obtain the printed board assembly with high one-time welding qualification rate.

Description

technical field [0001] The invention relates to the technical field of SMT assembly technology, in particular to an assembly technology method based on fine-pitch QFN devices and ceramic-sealed QFP devices. Background technique [0002] Currently, digital and radio frequency printed board assemblies (PCBA) often use fine-pitch QFN packages and pottery-encapsulated QFP package devices in high-density layouts, and the two devices are reflowed together with other surface-mount devices on the board. Welding; and due to their respective characteristics, there are certain differences in the requirements for assembly, resulting in improper handling, which will not fully meet the problem of one-time qualification after welding. [0003] Fine-pitch QFN devices have the characteristics of small size, invisible pads on the abdomen, and easy oxidation of the pins. Generally, the traditional reflow soldering process can be used to achieve soldering. Improper handling of operation rules ...

AI Technical Summary

Problems solved by technology

[0002] Currently, digital and radio frequency printed board assemblies (PCBA) often use fine-pitch QFN packages and pottery-encapsulated QFP package devices in high-density layouts, and the two devices are reflowed together with other surface-mount devices on the board. Welding; and due to their respective characteristics, there are certain differences in the requirements for assembly, resulting in improper handling, which will not fully meet the problem of one-time qualification after welding.

[0003] Fine-pitch QFN devices have the characteristics of small size, invisible pads on the abdomen, and easy oxidation of the pins. Generally, the traditional reflow soldering process can be used to achieve soldering. Improper handling of operation rules such as soldering curves and inspection requirements will affect the soldering quality of the device, resulting in problems such as poor contact of the pins with the pad, tin oxidation on the pins, high voiding rate of the solder joints, short circuit of the pins, and poor quality of the solder joints. Inspection and other defects, resulting in low pass rate

[0004] Due to the large difference between the thermal expansion coefficient CTE of ceramic QFP devices and FR4, which is commonly used in printed boards, stress is prone to accumulate at the solder joints during the temperature cycle, causing fatigue fractures; gold-plated pins also need Carry out gold tinning treatment, tinning operation can choose manual tinning or tin pot tinning according to the situation, but manual tinning will cause pin coplanarity problems; at the same time, affected by the size of the layout space, soldering on the printed board When the pad package size is not much different from the lead size, there is also a certain degree of impact on solder joint inspection and long-term reliability