Thermal expansion coefficient CTE

Since this meta-substituted diamine was much more reactive than OFB, a variety of polyimides could be made, aUowing the synthesis of such structures as PMDA-PFMB, a polyimide with a very low thermal expansion coefficient (CTE) that may provide many advantages for microelectronic fabrication. Linear polyimide structures have generally been found to have low CTEs even when bulky groups were attached to the main chain. 

Lap shear test conditions are not really convenient in electronics involving small dice and two substrates with different thermal expansion coefficients (CTE). The stresses generated during the cure cycle by this CTE mismatch account for possible crack formation and delamination, which in turn may degrade the adhesive strength. The die shear strength method consists in the measurement of the force required to shear the die from the chip carrier. Although any die size can be used, a standard technique is to bond 1.27 X 1.27 mm non-functional silicon dice to silver-plated lead frames. 

Thermal expansivity is often referred to as the coefficient of thermal expansion or CTE by polymer scientists and in the older literature. The terms are used interchangeably in this paper. 

TABLE 4.10 Effect of talc (Mistrofll P403, median particie size of 7.8 (im) on the coefficient of iinear thermal expansion-contraction (CTE) of an HDPE (MFI 0.4)-based composite material containing a 40-mesh pine wood flour (up to 55% content w/w) and the talc [8]... 

CLTE coefficient of linear thermal expansion or CTE, coefficient of thermal expansion... 

Figure 6.3 shows the longitudinal and the transverse coefficients of thermal expansion (the CTEs) predicted using the Rosen-Hashin model. The component properties of the composite used are ... 

Thermal Expansion Coefficient. Sometimes referred to as the coefficient of thermal expansion (CTE) and refers to the total expansion of the lattice cell as a function of temperature. For oxides with variable oxygen stoichiometry, the TEC consists of the thermal expansion and the chemical expansion. The latter is the expansion due to changes in oxygen stoichiometry. In this text it refers to the total expansion. 

Historically, the properties that received the greatest amount of attention were the glass transition temperature, Tg, and the coefficients of thermal expansion, or CTEs, particularly in the z-axis. With the advent of lead-free assembly processes, other properties have increased in importance as well.The most notable is the decomposition temperature,Ta.These properties were described in more detail in Chap. 6, and will be discussed again in Chap. 10, which focuses on the impact of lead-free assembly on base materials. However, some additional information as well as examples of the test data are included here, as well as comparisons of some common material types. 

Decreasing Aa, the difference in the package and substrate thermal expansion coefficients, by carefully selecting the CTE of the package and substrate (see Secs. 57.5.3.1 and 57.5.1.1, respectively). 

---