A NEW METHODOLOGY TO PREDICT AND MINIMIZE MOLTEN SOLDER JOINT OPENS AND SHORTS DURING REFLOWAuthors: Mudasir Ahmad, Ken Hubbard, and Sue Teng
Company: Cisco Systems, Inc.
Date Published: 9/24/2006 Conference: SMTA International
Warpage of large packages places several constraints on the minimum standoff height that can be obtained without causing shorts (bridging) and opens during reflow. This constraint will become even more of a concern as these large BGA packages migrate to finer pitches, i.e. below 1 mm pitch.
To ensure good solder joint formation and prevent solder bridging, it is critical to understand the amount of paste volume needed during assembly and reflow. The final shape of the solder joint is a function of surface tension, wetting area, gravity and applied forces. In this study, a new methodology to simulate solder joint shape is presented. Large deformation viscoplastic finite element analysis is used to simulate incompressible fluid flow.
The effects of package weight, solder volume and pad size on solder joint shape are analyzed. Different combinations of the design variables were simulated and functional relationships developed based on multivariate polynomial regression. The combination of design variables that can cause bridging in lead free solders are outlined. The amount of warpage over different lengths for 1mm, 0.8mm and 0.5mm pitch solder joints that can cause bridging is provided. The relationship between warpage and standoff height and maximum diameter is also provided for the different pitch values. This can be used to determine how much effective warpage would be acceptable to achieve a desired standoff height and maximum diameter.
Finally, a method to predict solder joint opens is outlined and compared with another known and validated shape prediction method (Surface Evolver ). The amount of displacement needed to cause a solder joint open is outlined.
ball grid array, coplanarity, eutectic solder, finite element analysis, high lead solder, hydrostatic pressure, leadless, microelectronics, micro lead frame, packaging, perzyna, rigid plastic, solder joints, shape, standoff height, surface evolver, viscoplastic, von Mises, warpage, pitch
Members download articles for free:
Not a member yet?
What else do you get when you join SMTA? Read about all of the benefits that go along with membership.
Notice: Sharing of articles is restricted to just your immediate work group. Downloaded papers should not be stored on an external network or shared on the internet.