Technological Improvement And Reliability Study On Reflow Welding Of High-density Multi-layer PCB Assemblies

There is large quantity of electronic products in aerospace industry and military field,which is an important composition of aerospace industry and weapon system.PCB assembly is essential to electronic products and its reliability of assembly and welding will directly decides the success or failure of products and missions of aerospace and military field.Since the issue and implementation of ROHS and WEEE instructions,only aerospace and military filed,which have high requirement on reliability,are using electronic components with lead.However,the European and US countries blockade on techniques and forbid any shipment of electronic components at military level or above to China.Therefore,most of imported components used in military filed are industry level and some are even electronic components without lead in business level.It brings an inevitable difficult of mix assembly of electronic components with lead and that without lead.Besides,there is urgent requirement in miniaturization,light-weight and multi-function of electronic products in aerospace and military field so the reflow welding techniques are widely used in aerospace models.As the complication degree of PCB assemblies increased,the original extensive reflow welding method and its management control method can't meet requirement of reliability on high-density multi-layer PCB assemblies.It's urgent to carry out technological improvement and reliability study on reflow welding of PCB assemblies to solve the current reliability problem of assembly and welding in models and products.This paper is based on techmological state and characteristics of current domestic aerospace and military field,and analyze in details the coating of solderpaste,installation of components and reflow welding process and conclude a set of reasonable and feasible technological parameters:select backward compatible mixed assembly plan to adjust the hole opening method and scale of silk print template of solderpaste,amend the patching method of patching device and adjust the technological parameters of hot-wind reflow welding oven so as to make the qualification of delivery inspection reach 100%;PCB assemblies manufactured with improved assembly and welding method can meet requirement of reliability on products.After test verification,it can fully prove that the improved reflow welding can solve the reliability problem ofhigh-density multi-layer PCB of electronic products and its engineering experience and technological parameters can be used in the assembly and welding of high-density multi-layer PCB assemblies in further manufacture.The research improves the reliability of assembly and welding of high-density multi-layer PCB,shortens the R& D period of products and greatly enhances the technological capability.The research method and concept can be used as reference to other technological improvement of PCB assembly and welding in other specifications.