Delamination moisture absorption

Of these failure mechanisms, the major ones associated with delamination include contaminated surfaces, inadequate adhesive coverage, stresses, voids, and moisture absorption. Many of these mechanisms are also responsible for other failure modes besides delamination. 

Besides delamination, actual cracking of silicon die is a failure mode that can occur from excessive adhesive stresses, voids, and moisture absorption. Residual stresses in adhesive-attached single-chip devices become critical as the size of the device increases and dissimilar die and leadframe materials are used. Several types of fractures that can occur within the die or within the adhesive are shown in Fig. 6.8. A hairline crack in an 1C chip that resulted from adhesive stress is shown in Fig. 6.9. 

Electromagnetic waves Electromagnetic wave reflection, absorption and transmission coefficients Dielectric properties (permittivity, loss factor), moisture absorption, delamination, geometry, flaw size... 

Other important properties include Z-axis expansion characteristics, moisture absorption, and adhesion characteristics within the material, commonly measured using time-to-delamination tests such as the T260 test. The Tg and its impact on Z-axis expansion are summarized below along with the decomposition temperature.The other properties will be discussed in Chaps. 8 and 10. 

In addition to providing circuit interconnection, a multilayer printed wiring board (ML-PWB) provides the electrical and mechanical platform for the system. This means that the electrical and thermal properties of the ML-PWB material are very important for the proper functioning of the system. Among the properties of importance are dielectric constant, Du (also known as Er) dielectric loss, Df (or tan 8) glass transition temperature, Tg time to delamination,Txxx thermal decomposition temperature.Ta coefficient of thermal expansion, CTE and moisture absorption. The following sections discuss the importance of these properties to an ML-PWB snbstrate. 

Hooper SJ, Toubia RF, Subramanian R (1991b) Effects of moisture absorption on edge delamination, part I analysis of the effects of nonuniform moisture distributions on strain energy release rates. ASTM STP 1110 89-106... 

All three occurrences have been known to lead to mechanical degradation. Moisture absorption can also contribute to the disruption of conductivity in the path between mating electrodes. This may include, for example, changes in the polymer/filler dispersion state through the expansion of the polymer matrix and formation of defects like cracks and delaminations. 

Moisture is absorbed by adhesives and other plastic materials to various degrees and can accumulate in voids within the bond line during assembly, testing, and operation. The absorption of moisture in adhesives as well as in other polymeric materials, such as molding compounds, has been proven to cause failures when parts are subsequently solder reflowed and exposed to the high solder melt temperatures of 200 °C and above. The rapid evaporation and expulsion of the moisture result in stresses that cause cracking and delamination, a phenomenon referred to as popcorning. 

The combination of absorbed moisture and temperature fluctuations can cause cracking and other damage. Sometimes, the matrix itself absorbs only a small amount of moisture and at first, the laminate behaves similarly, but at a late stage, when cracking in the interface region occurs, or there is delamination or translaminar cracking between plies, an unexpected increase in the laminate s overall absorption is noticed. 

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