Deformation Measurements used for Design Optimization and Verification during Industrial Electronic Board (Product) Manufacturing

Abstract

Thermo mechanical stresses in electronics can be calculated by FEM but sometimes it is faster and more comfortable to Measure the deformations of your Boards and electronic Components to see their behavior if temperature is changing. During the electronic product lifetime the soldering process is the highest thermo mechanical stress. Especially for the lead free reflow peak of more than 240degC some material combinations show a large deformation. But also later in the field at customer side the time to failure is depending from the stress & strain to the product. The differences day/night and operating/standby cause a thermo mechanic cycling and products fail if materials are getting tired and function fails. Beside other processes like diffusion and migration tins thermo mechanical stress can lead to early life time end. So it is important that the thermo-mechanical deformations are minimized and risks are noticed right in time - if possible during prototype stadium - where normally a high pressure of time and a quick measurement technique is welcome. The trend to higher application temperatures (e.g. Automotive sector: engine control) also is a main reason to care about tins land of optimizations. Due to the fact that the electronic board manufacturing in the assembly lines are consisting of many single processes but the components from the different suppliers are not known in regard to their material details and compositions, it's often not possible to start a simulation, which delivers true results, but it's much easier and faster to do a deformation measurement as a function of temperature. Three different measurement techniques (methods) are introduced: Shadow Moire or Interference Technique; Pattern Correlation Technique: Line Projection Technique. Finally some results are shown and examples from Siemens Product optimizations are given (comparison of different board materials/manufacturers, effect of preconditioning (tempering) to the warpage behavior of PBGA. examples of failures & failure modes if stress/strain is too high). Of course the measurement results are used to confirm the FEM results (No FEM without verification) and support DOE. But our experience is, that this methods of the quick measurement of deformations is used mainly as a tool to perform a kind of incoming inspection of delivered supplements like packages and boards. Often a poor thermo mechanical behavior could be proved and any changes of package properties of different date code lots could be recognized. If those male functions are detected before products reach our customers a lot of money (rework) could be saved and products of high thermo mechanical stability with few internal stresses could be delivered to market. The ratio of winning knowledge to examination costs is very high and the deformation measurements are used in all sectors of electronic product manufacturing.