Microprocessor and ASIC designers must focus on the thermal and mechanical IC die while considering the system cost and reliability. Covers and radiators are common solutions for mechanical protection. To ensure reliability, designers seek to minimize the junction temperature of die and often consider a high thermal conductivity to the most important attribute of the lid material. However, thermal performance and reliability depends on other factors: match or mismatch of coefficient of thermal expansion (CTEs) between the cover and mounting hardware, stiff cover / flatness, weight, dimensional tolerances and package design. thermal management techniques MANAGEMENTThermal provide heat dissipation without adding mechanical stress to the IC from thermal expansion differences between the IC, cover, substrate, interface materials, and other materials in the package. The materials cover the most common for microprocessors and ASICs are copper (Cu), aluminum (Al), silicon carbide and aluminum (AlSiC). With a thermal conductivity value of about 400 W / mK at room temperature, copper has the highest thermal conductivity of materials available. The thermal conductivity AlSiC and wrought aluminum are 190 and 200 W / mK, respectively. Designers should also consider issues associated with thermal cycling values CTE of the die and the lid, and other combinations. CTE is usually not a problem with a die size of less than 5 mm and heat flux less than 10 W/cm2. As the chip size and increase the heat flow, the differences between cover ETC, die, lid flatness, and weight have a significant effect on thermal performance, and selecting a cover material with a CTE compatible with the matrix becomes important. Compatible with material values lid CTE will reduce the bending of the Assembly and distortions die during thermal cycling. Comparing the average values of CTE of the lid and equipment common to die at 150 ° C, the closest AlSiC materials based on gallium-IC. A solder connection between the lid and die yields maximum heat dissipation in the flip-chip applications. The ETC AlSiC slightly higher in the chain is slightly compressed during assembly and thermal cycling. However, higher CTE materials can transmit catastrophic tensile forces on the IC with temperature. In any event, the game more AlSiC CTE is to minimize distortions package during assembly and thermal cycling. With twice the CTE AlSiC, copper leads to greater flexion of the system, but it has a higher thermal conductivity. Aluminum, with a 23-ppm / ° C CTE, is unfit for high power applications due to the large CTE mismatch. MATERIAL DENSITYAnother review is the matter density of the cover. Density (weight) is not a thermal property, but may affect protection of dying during assembly and service. Consider the weight per solder ball of the IC. During installation, the weight cover up can deform solder balls during creep soldering material (). It can also cause short circuits between the balls. In high-speed automated assembly, the weight of the lid has a significant influence on the package stress during the acceleration / deceleration quarters of the Assembly. Cover weight also affects shock and vibration and stress state orientation package for the service. These situations favor materials with a lighter weight. Weight is more important for larger meetings with covers over 40 mm2. ASSEMBLIESAs systems become larger, the combination of cover materials, shape, stiffness, flatness, and dimensional tolerances becomes as important as the values of thermal conductivity and CTE. Rigidity and dimensional tolerances to affect the cover of the chain. The depth of the cavity cover is important to minimize the gap between the die and the lid. This depth, a bit of flexibility depends cover, must be large enough to protect the die. For more rigid material, a lesser depth is acceptable, that the stiffness will not distort the eyelid during assembly, the fixing of the heatsink, and / or service. increases the rigidity of Lid-material with the thickness of the cover, but this may not be acceptable due to weight constraints. With a cover less steep, designers may need to impose more stringent dimensional depth of the cavity to maintain an acceptable bond line thickness. However, tighter tolerances increase the cost of manufacturing the lid. MANUFACTURABILITYManufacturing process and costs are other considerations in the choice of cover material. Each material has a preferred manufacturing process for the lowest cost, but the designers must take into account the costs of the entire system, including the rate of quality. A method of manufacturing low cost, stamping lids from sheet materials is the conventional method of manufacturing of copper and aluminum covers, limiting them to 2D shapes and especially with little 3D. Lids are stamped aluminum targets low power applications only because of high CTE and low thermal conductivity of aluminum. When dying is low or low-power, covers stamped copper can provide a cost effective solution. AlSiC uses a method of casting a bit more expensive but offers more features geometric shape. In addition to its compatibility with the materials ETC IC AlSiC also allows larger eye due to a lighter weight and more rigid.