■ Introduction of Electronic Packages

In the integrated circuit packages,the packaging material is responsible for supporting the semiconductor chip,protecting the chip,provide effective heat dissipation from the chip,chip insulation and have a effective means of connecting the external circuit and optical circuit.

■ The Features of Si/Al Packaging Material.

The controlled expansion (Si/Al)alloy encapsulation material has various of performance advantages, comprising the high thermal conductivity,low dielectric constants,low dielectric loss,high frequency,high power and etc. In addition,the thermal expansivity(CTE) of Si/Al alloy material is eminently suitable for the chips,in avoid of the thermal stress damage;the benefits of high stiffness and specific strength,not unduly hard, plays a vital role in protecting and supporting the chips;on account of lower cost,the aluminum-silicon alloys are being increasing used in commercial applications and allied industries;the Si/Al alloy material are in growing demand in aerospace and mobile telecom devices.

■ Applications of Si/Al Packaging Material

On account of outstanding comprehensive performances,the controlled expansion(Si/Al) alloy electronic housings or packages has a board application in electronic field,especially are being exploited in aerospace and military electronics.

■ The Preparation Technologies

The different methods of Si/Al alloy compound material in preparation process,it mainly contains casting,impregnation method,powder metallurgy,vacuum hot pressing,spray deposition and etc.

■ Casting Technology

Process description

A foundry is a factory that produces metal castings.Melting is performed in a furnace,in the metalworking,metals are cast into shapes by melting them into a liquid,pouring the metal into a mold,which contains a hollow cavity of the desired shape and removing the mold material or casting after the metal has solidified as it cools,the solidified part is ejected or broken out of the mold to complete the process.The basic process includes melting,mold filling,casting solidification and cooling.

Features include

- Advantageous:Simply devices,affordable cost,achieve the massive production

  - Drawback:The microstructure of primary silicon is coarse,this factor leads to poor toughness and ductility.

■ Impregnation Method 

Process description

Porosity sealing, also known as vacuum impregnating, metal impregnating, polymer impregnating, and porous metal sealing, is the process of filling a porous substrate to make it airtight.

Features include

-Advantages:Simple process and lower cost.

-Disadvantages:Due to the poor wettability between the aluminum liquid and the silicon matrix, the infiltration technology is difficult;the pressure system of the pressure infiltration is complex, which limits its industrial application.

■ Powder Metallurgy(PM) Technology

The powder metallurgy(PM) is a industry-leading technology,which regarded metal-powder or non-metal powder(or composition of metal-powder and non-metal powder) as the raw material,the process generally consists of powder blending (pulverisation), die compaction, and sintering three basic steps to fabricate metal or composition material and various components.The Basic Process of Powder Metallurgy totally has three basic steps which includes powder blending (pulverisation), die compaction, and sintering.

Features include

-Advantages:The microstructure of Si/Al alloy is equiaxed,homogeneous grains and the performance is stable.

-Disadvantages:By comparision, the technology has complicated process,higher compression moulding cost,limited by large scale.

■Vacuum Hot Pressing(VHP)

Hot pressing has a limited field of application for such materials which do not sinter to full densities due to low diffusion coefficients or for cases where a pore-free state is required (for optimum mechanical, thermal or optical properties).The Vacuum Hot Pressing is exploited as a technique for making powder metal(and ceramic powder) targets which are near-net-shape and high density. With this process only parts with simple shapes like plates, blocks, cylinders can be manufactured easily. With a highly sophisticated design of pressing dies also more complex shapes can be produced.

Hot pressing technology is applied variously in fundamental research and production.

The Process of Vacuum Hot Pressing

The Vacuum Hot Pressing process,it comprises heating,vacuum press with a specific temperature and post-treatment.

Features

-Advantages:The material is fabricated to be compactness,enhance the comprehensive performance of this material.

-Disadvantages:Higher cost,and the technology has a limited field of applications.

■ Spray Forming Technology

Introduction of spray forming technology

Spray forming, also known as spray casting, spray deposition and in-situ compaction,is a method of casting near net shapemetal components with homogeneous microstructure via the deposition of semi-solid sprayed droplets onto a shaped substrate. In spray forming an alloy is melted, normally in an induction furnace, then the molten metal is slowly poured through a conical tundish into a small-bore ceramic nozzle The molten metal exits the furnace as a thin free-falling stream and is broken up into droplets by an annular array of gas jets, and these droplets then proceed downwards, accelerated by the gas jets to impact onto a substrate. The process is arranged such that the droplets strike the substrate whilst in the semi-solid condition, this provides sufficient liquid fraction to 'stick' the solid fraction together. Deposition continues, gradually building up a spray formed billet of metal on the substrate.

Features of Spray Formed Process

-Advantages:These is a flexible process and can be used to manufacture a wide range of materials, microstructural aspects offer advantages in material strength because of fine grain size,refined distribution of dispersoid and/or secondary precipitate phases,the microstructure has surface roughness and no macro segregation.

-Disadvantages: It is hard to control the process,the complicated parameters,need to post-treatment.

■  Spray Formed Si-Al alloys for electronic packaging applications

Alloys containing up to 70wt%Si are being manufactured by spray forming. These alloys offer a unique combination of low thermal expansion, high thermal conductivity and low density, and are under investigation for electronic package thermal management applications in the avionics, satellite and other industries. The research concerns the characterisation of the key mechanical and microstructural properties of Al-70Si; the optimisation of spray forming; and the enhancement of alloy properties by ternary alloy additions and novel variants of the spray forming process. (Funded by EPSRC and Osprey Metals Ltd).

■Industry Chain Structure For Aluminum Silicon Material

■The main manufacturers of Si/Al alloy

The mainly manufacturers for the silicon aluminum alloy include Osprey in British,TTC and ©CPS,Denka in Japan and so on.Osprey company has been fabricating exclusive portfolio of controlled expansion(CE) alloys which has a dominate effect in the global market.

The silicon aluminum(Si/Al) alloy has a large commercial applications extremely used in radar components of the hermetically microwave packaging, optical-MEMS, EADS-Artis4 satellite microelectronics circuits, Raytheon (Raytheon) space and military aircraft and etc.

■Homemade manufacturers for Si/Al alloy

About the preparation process for the packaging material is still in the phase of researching and development,such as the mainly institutions and enterprises as the following,

Institution:General Research Institution for Nonferrous Metal;Institution of Ordnance Industry 52 in China.

Enterprise:Tianjin Baienwei New Material Technology Co.,Ltd.