Catherine Munier

Durability modelling of a BGA component under random vibration

This study introduces a computation method to assess damage in electronic solder joints under random vibration. It addresses full 3D dynamic behaviour of electronic board. Finite element modelling (FEM) of electronic BGA (ball grid array) and CGA (column grid array) packages assemblies are developed and adjusted with experimental modal identification of the test board. Vibration FEM simulations are performed to calculate stress transfer functions of critical solder joints. Then, solder joint time-stress responses due to an input random excitation of the board are generated. Stress range distributions are established from rainflow counting. Finally, linear damage computation is done and compared with experimental results by using an empirical damage law. The potential and the limitation of this method are discussed.

Modelling of Sn3.0Ag0.5Cu thermo-mechanical behaviour by a continuum damage approach

A continuum damage model is proposed for Sn3.0Ag0.5Cu solder alloy in pure shear conditions. Experimental tests were performed on specific torsion samples to adjust material parameters of the continuum damage model. The main advantage of this method is to introduce damage process in the mechanical behaviour law of SnAgCu solder. Damage process highly affects the mechanical behaviour of solder alloy during thermal cycle fatigue. Thus, the lifetime of solder can be estimated by using this model without the determination of fatigue laws.

Sn3.0Ag0.5Cu solder joints lifetime estimation for electronic assemblies under random vibration

This study presents a method to assess component durability under random vibration according to board design and package specificities.Experimental tests were performed and times-to- failure (TTF) of several components were recorded. Consequently, failure modes of packages were identified. A complete FE (finite element) board model with 3D packages of CICGA (ceramic interposer grid array), PLCC (plastic leaded chip carrier) and FBGA (fine ball grid array) components was built. Dynamic behaviour of the board was adjusted with experimental measurements. Transfer functions in stress in critical solder joints were thus calculated for five components. Finally, a damage estimation, which consists in the generation of time-stress responses, was performed. Rainflow cycle counting, linear summation and Basquins equation were used to compute the elastic damage accumulation in solder joints. Results were confronted and adjusted with experimental TTF. The method is explained and results are discussed.

Thermo-mechanical simulation of a SiP (System-in-a-Package) LGA (Land Grid Array): Impact of the internal IC (Integrated Circuits) on the 2 nd level solder joint reliability

System-in-a-Package (SiP) aims to integrate a functional sub-system with one or more semiconductor chips along with passive components onto a substrate. SiP is transferred molded to the OEM for second level assembly using industry standards and high volume equipment. In most recent applications (high I/O density, improved electrical performance), LGA (Land Grid Array) is a very practical solution for the 2nd solder joint level. LGA packages reduce integrated circuit mounted height by eliminating the solder balls that are used for mounting BGA (Ball Grid Array) packages to system circuit boards. Instead, LGA packages are reflow-mounted using solder that has been applied to the board.

Flexible test bench to study the reliability of electronic assemblies

Robustness and reliability for electronic boards are key issues, especially in the aeronautics industry. To study the reliability of the assembly, accelerated tests are performed on daisy chain components assembled on Printed Circuit Board (PCB). Times to failure of components need to be accurately detected to propose relevant fatigue and reliability models. To electrically monitor the daisy chains, a flexible event detector has been developed by EADS Innovation Works. Its aim is to detect micro-events in a solder joint. Indeed, despite the crack initiation and propagation, the solder joint can still conduct electrical current intermittently. Nevertheless, the solder joint is not considered as reliable because it is not able to fulfill its function in any case. Firstly, this paper presents the characteristics of the flexible event detector. A part of the system records continuously micro-events, for a large number of channels. Then, a custom interface analyse the data recorded by the multi channels system to identify those which correspond to standards (such as IPC-SM-785) or a custom criteria. To illustrate this method and validate the event detector, some experimental vibration tests were performed. Several components electrically failed during the tests and were precisely detected by the flexible event detector. Finally, a comparative vibration testing is performed between a commercial event detector system and the EADS IW one to identify the detection capacities of each solution.