Crack in Aramid Fiber/Epoxy Matrix Interface

Crack in Aramid Fiber/Epoxy Matrix Interface

Material Name: Solder
Record No.: 167
Primary Chemical Element in Material: (Cu)
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: Another factor determining the solder joint strength of components in products is the build-up layer under the pad because of its effect on the peel strength. Aramid. and resin coated copper (RCC) on FR-4 are currently widely used for the build-up layer. Chopped, short Aramid fiber reinforcement is used due to its unique advantage of low in-plane coefficient of thermal expansion (CTE), excellent dimensional stability, highspeed laser and plasma processability, and low dielectric constant. Although Aramid reinforcement is an excellent choice for low CTE and micro via technology applications, potential disadvantages include susceptibility to moisture and weak fiber-matrix interface. An example of cracking in the Aramid layer due to weak interfacial bond between the Aramid fiber and the epoxy matrix after PWB exposure to mechanical impact is shown in Figure 1a. Such cracking in the build-up layer can cause electrical failure when the crack surfaces outside the pad and severs the trace as shown in Figure 1b. Therefore, the shear strength of Aramid build-up samples is compared to an alternative, resin coated copper (RCC).
Reference: Sridhar Canumalla, Hee Dong Yang, and Puligandla Viswanadham, Method for Measuring Package to Board Interconnection Shear Strength for Area Array, Fine Pitch Packages, ISTFA 2002, Proceedings of the 28th International Symposium for Testing and Failure Analysis, 3-7 November 2002, Phoenix Civic Center, Phoenix, Arizona, pp. 377-384.

Figure 1: a) Crack in the build-up layer caused by debonding of the aramid fiber/epoxy matrix interface, b) the crack in the build up layer surfaces near the periphery of the pad to cause trace breaks.