Study On Ultra-fine-pitch Wire Based On The Photolithography And Electroplating Technology

With the advent of the 5G era,the microelectronics industry is increasingly demanding high integration,high reliability and small size.This puts higher demands on the electronic packaging industry.The high density,high reliability and low cost requirements of packaging technology are driving the development of finer leads and higher I/O quantities.At present,the most commonly used packaging technology is wire bonding.The continuous reduction of wire width and pitch brings certain difficulties to the design of the bonding machine,and this also causes problems such as reduced bonding strength and short circuit of leads.This brings great challenges to wire bonding.So the research on the new method for realizing ultra-fine lead is of great significance.This paper creatively proposes a method for making ultra-fine lead structures based on photolithography and electroplating processes.It can replace the wire bonding to achieve the connection between the chip and the substrate.In this way,the size of the leads can be further reduced to the precision of lithography,which is good for high-density packaging.Firstly,for the reliability requirements of high-density packaging,especially the limitation of thermal stress on the feature size of the lead,the internal stress of the structure with different wire width,pitch and length under temperature change is analyzed.According to this,the range of lead size parameters whose internal stress level can meet the reliability requirements is determined.This provides a basis for subsequent lead structure design and corresponding process research.On this basis,the fabrication process of ultra-fine suspended lead structure was studied for the requirements of high-density packaging.In the suspended leads,the pads on the chip and substrate are not in the same plane,and the height difference is more than 20 ?m.In view of the above challenges of the three-dimensional microstructure features on the lithography and development process,this paper proposes to use dry film instead of the conventional liquid photoresist.This solution solves the problem of profile coating,film quality control and compatibility with the sputtering process.On the basis of process optimization,the non-planar pattern transfer problems in the fabrication of the pads and the wire are overcome by the optimization of the exposure,development parameters and mask patterns.The selective release of the suspended lead wire is realized by the layer-by-layer etching,temperature adjustment,the etching liquid formula and the stirring condition,etc.Finally,the complete process of ultrafine hanging leads was successfully researched,and ultra-fine lead samples are successfully fabricated.The test results show that the prepared lead structure can be finer than the conventional wire bonding.The lead width can be reduced to 10 ?m.And the pitch of the lead structure can be finer than that of the conventional wire bonding.The pitch of 20 ?m wire can be fined to 25 ?m.It is only 1.25 times the line width,which breaks the limit at least 1.5 times in the conventional wire bonding.In addition,the wire length can be controlled more flexibly,and it can be 50?m or even shorter.Finally,the bonding force of the lead structure is tested.The bonding force of different size lead structures was measured to be above 0.1 N,which is close to the bonding level in the traditional wire bonding technology.