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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