DFN1610 Design And Implementation Of Voids Control In Adhesive Layer

The QFN(Quad Flat no-lead package)is one of the small signal discrete semiconductor device,we call it DFN when it is rectangular in shape,it represents the most advanced form of packaging in surface mount technology.DFN1610 TVS(Transient Transient-Voltage-suppression)diode is one of them.The package uses a silver paste soldered process to increase production efficiency by adding silver powder epoxy to the chip and bonding to the substrate,taking advantage of the epoxy's ability to cure quickly,thus,a more practical and more reliable pin-free package device is obtained.There are two kinds of semiconductor welding processes at home and abroad: EUTECTIC welding and silver paste welding.EUTECTIC welding is through setting the fixed high temperature conditions,so that the metal at the bottom of the crystal and the base metal to form eutectic.Silver Paste welding is to grab the cut crystal and place it on the substrate with silver paste,and then use the appropriate temperature to quickly bond the chip to the substrate.Compared with eutectic welding process,silver paste welding process adopted by DFN1610 is more likely to produce uneven distribution of silver paste layer,partial bubble or incomplete covering,etc.,the formation of cavity will lead to the heat of the device gradually concentrated in the cavity layer during the later use of the device,which can not be effectively dispersed out.When the converging hot spot reaches a certain height,it is easy to cause the device to be broken down by heat,affect the reliability of the device.The void formation of DFN1610 adhesive layer is affected by many factors,mainly raw materials and production process.The raw materials mainly include the frame with pre-plated metal layer,the silver paste and the chip with back metal layer.In this paper,the related factors are further analyzed and a large number of experiments are carried out to explore the different modes and principles of the influence on the voids in the adhesive layer.At the same time,the correlation between silver paste fluidity and EBO(An organic substance that prevents the diffusion of water in silver pulp)was studied by using auxiliary equipment water drop angle equipment,and the failure mode of product voids was detected by X-Ray equipment.In addition,the chip with back AU and back Ag are compared,and the advantages and disadvantages of the chip with back AU are found: The chip with back AU is more favorable for silver slurry overflow,the chip with back AU can control the rise of silver slurry,and the chip with back silver has a silver curling edge after being cut,the overflow of the silver slurry is restrained,creating the risk of the silver slurry climbing and hollowing out.At the same time,we try to find a better scheme to improve the quality of the chip with back-Ag.We use the back-Ag thinning process to produce the sample.At last,we select the suitable raw material,the reasonable chip bonding method,the effective monitoring method,and reduce the productivity of voids,the control of the voids is completed: the target of < 5% of the single void area and < 15% of the overall voids area is achieved,so as to achieve the successful mass production.