Cisco Systems, Inc.

Transient Solder Separation of BGA Solder Joint During Second Reflow Cycle

May 15, 2019 | Steven Perng, Weidong Xie

As the demand for higher routing density and transfer speed increases, Via-In-Pad Plated Over (VIPPO) has become more common on high-end telecommunications products. The interactions of VIPPO with other features used on a PCB such as the traditional dog-bone pad design could induce solder joints to separate during the second and thereafter reflows. The failure has been successfully reproduced, and the typical failure signature of a joint separation has been summarized.</p><p>To better understand the solder separation mechanism, this study focuses on designing a test vehicle to address the following three perspectives: PCB material properties, specifically the Z-direction or out-of-plane Coefficient of Thermal Expansion (CTE); PCB thickness and back drill depth; and quantification of the driving force magnitude beyond which the separation is due to occur....

Enhancing Mechanical Shock Performance Using Edgebond Technology

Jun 26, 2014 | Steven Perng, Tae-Kyu Lee, and Cherif Guirguis - Cisco Systems, Inc., Edward S. Ibe - Zymet, Inc.

Edgebond adhesives have been widely used by the industry for improving the shock performance of area array packages. Most of the studies focus on the impact of material properties, such as coefficient of thermal expansion (CTE) and glass transition temperature (Tg), on reliability at room temperature. However, the operating temperature of a component on the printed circuit board bonded with edgebond adhesive can be close to or exceed Tg of the adhesive, where the material properties may be very different than at room temperature....

Determination of Copper Foil Surface Roughness from Micro-section Photographs

Apr 25, 2013 | Scott Hinaga, Soumya De, Aleksandr Y. Gafarov, Marina Y. Koledintseva, James L. Drewniak

Specification and control of surface roughness of copper conductors within printed circuit boards (PCBs) are increasingly desirable in multi-GHz designs as a part of signal-integrity failure analysis on high-speed PCBs. The development of a quality-assurance method to verify the use of foils with specified roughness grade during the PCB manufacturing process is also important... First published in the 2012 IPC APEX EXPO technical conference proceedings....

Investigation of Pad Cratering in Large Flip-Chip BGA using Acoustic Emission

Jan 03, 2013 | Anurag Bansal, Cherif Guirguis, Kuo-Chuan Liu

Electronics assemblies with large flip-chip BGA packages can be prone to either pad cratering or brittle intermetallic (IMC) failures under excessive PCB bending. Pad cratering cracks are not detected by electrical testing or non-destructive inspection methods, yet they pose a long term reliability risk since the cracks may propagate under subsequent loads to cause electrical failure. Since the initiation of pad cratering does not result in an instantaneous electrical signature, detecting the onset of this failure has been challenging. An acoustic emission methodology was recently developed by the authors to detect the onset of pad cratering. The instantaneous release of elastic energy associated with the initiation of an internal crack, i.e., Acoustic Emission (AE), can be monitored to accurately determine the onset of both pad cratering and brittle intermetallic (IMC) failures....