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FROM: I. MEMIS, DEPT GGMG/BLDG 257-4, AISLE A, ENDICOTT                        
      ENDICOTT ELECTRONIC PACKAGING                                            
SUBJECT: CTE Values for PWB                                                    
The previous postings are atttached.                                           
 ______________________________________________________________________        
                                                                               
 The problem mentioned requires accurate local CTE values.  For a PWB,         
 CTE changes after each process such as drilling through holes, filling        
 the holes with solder, copper plating etc.  The PWB CTE also changes          
 with it's geometry.  The entire PWB area of interest must be measured         
 to accurately assess CTE impacts in the area of components and other          
 features such as heat sinks.                                                  
                                                                               
 Advanced computational mechanics tools such as the                            
 Finite Element Method (FEM) are tempting for CTE                              
 determination.  A numerical prediction of CTE, however,                       
 requires accurate assessment of material properties such as                   
 Youngs modulus, Poissons ratio, CTE etc. and the linear or                    
 nonlinear constitutive relationship of each material used in the              
 component.  The in-situ material data, especially temperature-                
 dependent material properties and nonlinear constitutive                      
 relationships, are not readily available in the literature, which             
 makes prediction uncertain.                                                   
                                                                               
 Recently, moire interferometry was proposed as a tool for CTE                 
 measurement of electronic packaging components. The abstract                  
 of the paper can be found below.                                              
                                                                               
 ABSTRACT                                                                      
                                                                               
 Moire interferometry                                                          
 is a whole-field displacement measurement technique with a                    
 sub-micron sensitivity, which can produce the global CTE and                  
 the local CTE across the entire component with high accuracy.                 
 The large dynamic range of the method makes it compatible                     
 with CTE evaluation of a broad range of components.  Two                      
 experimental procedures were suggested for (1) CTE over a fixed               
 temperature range and (2) CTE as a function of temperature.                   
 The procedures are implemented for various thin small outline                 
 packages, a plastic ball grid array package and a stacked                     
 memory cube.  The results emphasize the importance of a                       
 whole-field measurement technique.  A supplementary TMA                       
 test on an aluminum alloy is conducted and the results are                    
 compared with a moire measurement to discuss the accuracy of                  
 the proposed measurement procedure.                                           
                                                                               
 {1} B. Han and Y. Guo, "Determination of Effective Coefficient                
 of Thermal Expansion of Electronic Packaging Components: A                    
 Whole-field Approach, IEEE Transactions on Components,                        
 Packaging and Manufacturing Technology-Part A, (submitted                     
 for publication), 1995.                                                       
                                                                               
KEY CONTACTS FOR MORE INFORMATION:                                             
   Bongtae Han, IBM ENDICOTT, 607-757-1077                                     
                INTERNET ID -  [log in to unmask]                               
   C.K. Lim   , IBM ENDICOTT, 607-757-1138                                     
                INTERNET ID -  [log in to unmask]                             
                                                                               
Previous Postings                                                              
-----------------                                                              
                                                                               
 We found that using TMA can be misleading, especially in an                   
 "unbalanced" design (e.g. amount of copper NOT symetric around the            
 center (thickness) of the board.  We found strain gageing both sides          
 of a PWB the only reliable way to get CTE data.                               
                                                                               
 Jim Maguire                                                                   
 Principal Engineer, E/E M&P                                                   
 (206)657-9063                                                                 
 Boeing Defense & Space Group                                                  
 [log in to unmask]                                                 
                                                                               
 Reza,                                                                         
 Might we be able to measure the CTE of this gentleman's boards using TMA?  He 
 may have coupons available...  It seems he is looking for an analytical means 
 to                                                                            
                                                                               
 predict CTE differentials.  Just a thought.                                   
                                                                               
 Phillip                                                                       
 ______________________________________________________________________________
 _                                                                             
 Subject: CTE Values of Printed Circuit Board and Heatsink combination         
 From:    [log in to unmask] at Internet                                          
 Date:    10/31/95  11:15 AM                                                   
                                                                               
 Help!                                                                         
                                                                               
 The Engelmaier equations used to estimate cycles to                           
 failure for leadless SMT components has, obviously, as                        
 one of it's terms the CTE of the printed wiring board.  I                     
 have been unable to obtain information on CTE of printed                      
 circuit boards, at least with any confidence, and                             
 measuring the CTE after build is too late in the product                      
 development cycle.  This is cirtical to our applications                      
 due to the long thermal cycling requirements of some of                       
 our programs (7-15 years).                                                    
                                                                               
 The CTE of the board is effected by:                                          
 Base Material (Kevlar, Polyimide, G10)                                        
 Resin                                                                         
 Materal Lot                                                                   
 Layer count                                                                   
 Amount of copper (planes)                                                     
 Heatsink bonding                                                              
 Heatsink bonding material (epoxy, acrylic, thermabond)                        
 Heatsink material (aluminum, copper)                                          
                                                                               
 1.  Has anyone done any testing on CTE of boards as a                         
 function of the above?                                                        
                                                                               
 2.  Are there any equations which can be used to predict                      
 the CTE of the board and/or heatsink combination?                             
                                                                               
 3. Is there any data on the CTE of boards besides the                         
 ranges I have seen in the text books.                                         
                                                                               
 I am considering running an experiment to determine the                       
 effects of these parameters.  Would anyone be interested                      
 in the data and of course help support the effort with                        
 boards, heatsink and bonding?                                                 
                                                                               
                                                                               
 Jim Faris                                                                     
 AlliedSignal Aerospace                                                        
 Guidance & Control Systems                                                    
 (201) 393-3779                                                                
                                                                               
USERID: MEMISIRV, NODEID: ENDVM5, TEL: 855-6022  FAX: 857-1126                 



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