Tony,

   Excellent report!  I am curious what your surface mount pad geometries
for wave solder on the 0805 and the case A Tantalum Caps were?

   Kimball Electronics Group Surface Mount Pad Geometries for

0805                                                                       

                                        WAVE SOLDER ATTACHMENT METHOD 
                 pad height: .060  pad width: .040                     
                 pad spacing from center to center: .090                

CASE A TANTALUM CAPACITORS                                                 
                    
                                        WAVE SOLDER ATTACHMENT METHOD 
                 pad height: .065  pad width: .065                     
                 pad spacing from center to center: .104                

=-=-=-=-=-=-
Tony wrote...

From: "D. A. (Tony) Stewart" <[log in to unmask]>                        
    
To: [log in to unmask]                                                        
    
<b> Subject: Solution: No Solder on Size "A" Tant Caps after WAVE also
SOT-23's      </b>
                                                                           
    
After building 4000 PCA's for a customer, which has 14 Case Size "A"       
    
Tant. Caps out of approx 400 parts on the wave side, it was found that     
    
PCA's averaged 14 "No Solders"/PCA after wave. (50% joints of 28 in        
    
random positions) Almost all the defects were on these Case Size "A"       
    
component types. Case size "D" Tant Caps and 805 ceramic parts were        
    
defect free. What is unique about Tant SM caps is that the leads only      
    
travel half-way up the body , unlike ceramic chips which terminal          
    
surround the ends. The Case size "D" had larger lands. Occasionally        
    
defects for excess solder were found as a result of trying to increase     
    
the  solder flow to these difficult parts. (eg slower feed rate, higher    
    
chip wave etc.  The SOLTEC wave soldering machine uses a foam fluxer (No   
    
Clean flux) with good foam height and bubble size. An experiment to hand   
    
spray flux reduced the qty of defects to 4/PCA, but did not make the       
    
process defect-free. (Yes we know foamers are not the best kind)           
    
To make the process Defect-Free and specifically free of "No Solder"       
    
joints, we measured a sample of exposed solder lands and checked a         
    
variety  OK and "bad (NS)" joints. The result was there were 0 joints      
    
with 0.060 (1.5mm) exposed lands that failed.  Since it was too late to    
    
change the pad design for this production run, we considered 1) do         
    
nothing except continued 100% inspection, 2) hand-solder both ends, 3)     
    
offset the part, leaving only one joint requiring hand solder.  This was   
    
considered better than leaving inspection to chance. To offset the parts   
    
0.5mm or 20 mil on the Fuji placement offset, would provide 100%           
    
probability of lead soldering . The pad size allows contact with the       
    
0.8mm (32mil) terminal length with the offset and then manual soldering    
    
of only 1 joint is required. This is expected to reduce the process        
    
variable of Case Size lead solderability to zero and make this part of     
    
the process defect-free.                                                   
    
                                                                           
    
Other Opportunities                                                        
    
====================                                                       
    
 Interesting enough we theorize this solution will fix SOT-23 "No          
    
solder" problems.  I've read the history of people who have had problems   
    
on this part.  If you can,  increase the land size to accomodate your      
    
wave soldering process or in the Size "A" Tant Case here .060" or          
    
1.5mm.  Don't put too much faith into IPC-782 design requirements. They    
    
are only guidelines.  Determine your own optimum LAND Designs and          
    
provide input to your customer's design.                                   
    
                                                                           
    
EXPERIMENTAL DATA                                                          
    
                                                                           
    
Exposed Lands  Inspected Joints to IPC class2                              
    
[thou]       [mm]  % bad % OK                                              
        
======   ===== ===== =====                                                 
    
0.000        0.00    100%     0%                                           
                
0.010        0.40    100%     0%                                           
                
0.020        0.80     50%    50%                                           
               
0.030        1.20      50%   50%   worst case                              
               
0.040        1.60      33%   67%   this is IPC782 guideline size           
               
0.050        2.00      43%   57%                                           
               
0.060        2.40        0% 100%   defect free on several batches inspected
                 
0.070        2.80        0% 100%                                           
                 
                                                                           
    
0.018        0.73     Kemet MIN. Land Length  Case size "A" Tant Caps      
           
0.031        1.23     Kemet NOM. Land Length                               
           
   Note that KEMET does not have a MAX!!                                   
    
0.040"       1     IPC782A MAX Land Length (calculated)                    
        
         Haven't checked Rev B yet                                         
    
0.060       1.5 mm    C-MAC MIN Land Length for No clean flux with foam
fluxer      
on SOLTEC wave                                                             
    
                                                                           
    
RSVP by e-mail                                                             
    
                                                                           
    
regards,                                                                   
    
Tony                                                                       
    
                                                                           
    
Eng Manager          Web:      http://cmac.ca                              
    
                                                                           
    
***************************************************************************
    

//-
Rich Everman    (tel) 812-634-4401    (fax) 812-634-4700
Kimball Electronics Group  -  -  http://www.kimball.com
PWB Component Engineer -   -  reverma@kimball..com
//-

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