High temperature alternatives to ball grid coplanarity measurements to improve correlation to surface mount quality

For many years the primary means of ensuring surface mount (SMT) quality of components has been monitoring outgoing coplanarity at the component factory. This method has been embodied in a collection of JEDEC and other standards. While this approach is successful in general it has one primary limitation, it is measured at room temperature. The lack of correlation to SMT quality leads to issues for false failure and false acceptance. The former issue can negatively impact component costs and can impede innovation in new packaging technology. The latter issue may lead to poor yields in board assembly and product delays. The trend toward lower profile or thin components often results in packages that inherently warp more than thicker components. Depending on the assembly methods and component design these packages can become very flat at reflow temperatures despite their high coplanarity values when measured at room temperature. In many cases component manufacturers have resorted to using stiffeners and heat spreaders as means of complying with room temperature coplanarity standards, despite the fact that this may not actually improve SMT and may degrade solder joint reliability. Alternately, there are many cases of false acceptance, due to packages that meet the room temperature requirement but fail to surface mount. In these cases, the components often increase in warpage during reflow. An alternative method is being proposed that would help to relieve the above issues. It involves several key elements. First, the component manufacturer should understand the warpage behavior of component with temperature. Second, provide alternative requirements in the standards. Third, provide means to adjust the coplanarity criteria for factory monitoring to suit the unique behavior of a specific device. In this paper the above elements are demonstrated with case studies. The first case study examines the correlation of coplanarity measurements to the high temperature warpage meas- rement. A novel temperature compensation method is proposed to set coplanarity monitoring requirements. These derived limits ensure that the factory process does not drift away from the characterized process and maintains the SMT quality. This method can be successfully implemented using existing factory equipment. The second case demonstrates the use of these new methods to establish the quality and reliability of a package with high room temperature warpage.