Mr. Franck, Mr. Paul, and others: Mr. Paul's last comment on the utility of the existing bow and twist measurement guidelines is an important issue. Mr. Paul noted (in general) that the test method should be used as a base line measurement for analyzing the effectiveness of process/material improvements. It is apparent that the existing guidelines and procedures surrounding bow and twist have two major shortcomings. First, the technique for measuring bow and twist is not exactly optimal. There is a large amount of operator dependency, measurements are made with mechanical/contact devices, and measurements are not made in a 'free state' (e.g. one must hold corners down, etc.). Second, information and know-how on bow and twist does not exist in a readily transferable knowledge base. It appears that most manufacturers are dependent upon certain key individuals with years and years of experience to identify causes of excessive warpage and to correct it. The problem lies in the fact that the decisions these key individuals make to solve problems are based upon something they have seen or done before. As effective as they may be in solving the problem, once the person is gone it is tough to replace them. A quantifiable knowledge base is not left behind for others to work with/from. A new technology developed at the Georgia Institute of Technology (Georgia Tech), Atlanta, Georgia, may help address the two issues outlined in the above paragraphs. A technique was developed which allows assemblers to monitor, in real-time, thermally induced warpage during processing (e.g. IR reflow, wave solder, convective reflow, UV cure, etc.). The technology was licensed to a spin-off, start-up company which has commercialized the measurement service under the tradename TherMoire. TherMoire incorporates a well known, and proven technique called shadow moire. Shadow moire is an optical technique which is capable of characterizing surfaces in the z-axis dimension. Basically, it provides a topographic map of large area surfaces, much like the contour maps produced by the US Geological Survey. Shadow moire has been used by the industry with success to study the effects of process/material variations on bow and twist in printed circuit boards/assemblies. The technique is superior to the existing IPC measurement technique for bow and twist for many reasons. Most notably, shadow moire is optical, non-contact, operator independent, and it allows for boards to be measured in a free state (e.g. just resting on a table top - or a calibrated slab of granite). Electronic Packaging Services, the company that spun off from Geogia Tech, has developed a modified version of TherMoire for production level usage. During the 1996 IPC Printed Circuit Expo in San Jose, CA, a prototype of a new system called LineMoire will be unveiled. LineMoire will be a production level, in-line, warpage measurement piece of equipment. LineMoire will be fully automated and capable of 100% inspection. LineMoire will not only accept/reject each sample based upon a pre-set parameter for bow and twist, but it will produce statistical analyses on frequency, magnitude, and LOCATION of bow and twist (sounds like a bow and twist SPC system to me). LineMoire can make local and global measurements on a surface. Local warpage information/data will only become more critical in the future. A sample application: LineMoire can analyze a large QPF interconnect area or say a BGA area for planarity prior to solder paste screening and/or automated pick and place. I encourage all to come by the booth at the IPC Printed Circuit Expo in March. As excited as we are about LineMoire, we need feedback from the technical community on how shadow moire techniques could potentially be used in a revision to IPC 2.4.22. Understandably, all IPC standards and approved techniques must be readily available to all. Challenges exist on how to make the data generated by shadow moire easily readable and techniques for interpretation more standardized. I look forward to meeting and working with many of you in the months ahead. Best Regards, Patrick Hassell Electronic Packaging Services (404) 881-1114 [log in to unmask]