Viscoelastic Effect of FR-4 Material on Packaging Stress Development

Abstract

In the microelectronics device, FR-4 material is one of the key component materials in the packaging structure. The structure of FR-4 is featured as a typical orthotropic polymer composite material reinforced with glass fiber. Although the material may exhibit viscoelastic behavior, the material is commonly regarded as temperature-dependent elastic one in the microelectronics reliability analysis. The purpose of this study is to investigate the material property modeling effect of FR-4 on the reliability prediction. To obtain the FR-4 material properties, a series of stress relaxation test was performed. Based on the data, the behavior of the FR-4 was modeled as orthotropic temperature-dependent elastic and viscoelastic. An analytical method was employed to calculate the engineering constants required for the calculations. The elastic calculation was performed by ANSYS, and the viscoelastic calculation by a FORTRAN program, respectively. The FORTRAN program was written separately, and capable of calculating the viscoealstic calculations when the material is orthotropic. Board on chip (BOC) packaging structure, a new type of the first level packaging for memory chip, was considered for the stress development analysis. The results were compared to examine the difference based on the FR-4 material property modeling.

Thermal-Performance Instability in Piezoresistive Sensors: Inducement and Improvement

“…Results show that the adhesive overflow can lead to 10% increase of thermal drift to the accelerometers [69]. Moreover, the viscoelastic behavior of PCB material (FR-4) also contribute to the thermal instability of piezoresistive sensors [70]. …”

Viscoelastic properties effect on solder ball failure analyses

“…Two different types of the molding compounds were characterized for the mechanical properties in the previous study [1,2], and named as molding compound A (MC-A) and molding compound B (MC-B). For the substrate, two different types of the materials (SUB-A and SUB-B) were employed, and their material properties were also measured in the previous works [2,4]. Through the stress relaxation tests, the mastercurves of the materials are obtained and represented in Fig.…”

“…The modelings are also shown by solid lines in Fig. 2, and the parameters of the Prony series and the shift functions are listed in the previous works [1,2,4]. The mechanical properties such as coefficients of thermal expansion (CTE) and Poisson's ratios of the molding compound, substrate, silicon, copper are listed in Table 1.…”

“…Two types of molding compounds and two types of substrates were employed, the mechanical properties of which were readily measured in the previous works [1,2,4]. The properties were modeled as conventional temperature dependent elastic as well as viscoelastic.…”

Warpage mechanism analyses of strip panel type PBGA chip packaging

“…Despite the fact that the substrate exhibits viscoelastic behavior [8][9][10], it has been modeled mostly as elastic [7,[11][12][13]. The first numerical study on the bare chip warpage development with viscoelastic FR-4 consideration was investigated by Kim [10]. Simultaneous consideration of the viscoelastic characteristics of the molding compound and the substrate in the warpage analyses was recently investigated by Kim and Lee using numerical approach for ball grid array chip [14].…”