Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Reflow of 0402 capacitors

Ralph Merk

#5500

Reflow of 0402 capacitors | 8 March, 2001

We are currently using 0402 resistors and capacitors in our production process. Our equipment is as follows:

- DEK 265 - Siemens S25/F5 - Vitronics XPM520(5 zones) - 2% silver solder Alpha WS678

The problem is that randomly some 0402 capacitors are unsoldered on one side. The resistors do not have this problem. The caps do not appear to be drawbridged, the solder deposit on the pad does not wet to the part. We have tried the following: Elevate and lenghten the soak time, peak temp of 220C, liquidous time of 50 sec, slope of 2-3 degrees/sec, use round pads with gold immersion finish, try 3 different manufacturers with varying results but no solution, 5 mil stencil with 15% reduced aperture, checked pad/trace design for uneven wetting forces-some problem parts had ground planes on one side-but some did not, placement accuracy is not an issue-this problem only manifests itself on the 0402 capacitors-not resistors. I am out of ideas, any suggestions would be welcome. Thank you.

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Dave G

#5506

Reflow of 0402 capacitors | 8 March, 2001

Have you considered a different solderpaste ? A different flux chemistry may help. The metals content wouldn't have to change. Just go after a slightly more aggressive flux.

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Arturo

#5507

Reflow of 0402 capacitors | 8 March, 2001

You did not mention to change the solder paste to another formulation or brand.We used to have that kind of non wetting problem on 0402 cap when we used Alpha's LR737(63/37) Type 4 No Clean and the solution was to change the solder paste to Alpha's LR725(63/37) Type 3 No clean. I know you are using WS but anyway you could try other suppliers to compare and discard this possibility.

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#5510

Reflow of 0402 capacitors | 8 March, 2001

Sounds like you've done a good job of troubleshooting.

Two thoughts are:

1 An alternative to using a hotter flux that the others mentioned is to use components with more solderable terminations. [A firm grasp on the obvious.]

2 You spoke about increasing temperatures on the profile. I wonder if you might be burning-up your flux before reflow. Would less heat help?

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CAL

#5513

Reflow of 0402 capacitors | 9 March, 2001

We have seen some problems with component end cap solder terminations not being symetrical. i.e. If one end on the cap has a larger solder ternination this sometimes is enough surface area during reflow to lift the opposite side of the component. We have noticed a larger precision variations between 0402 res. and 0402 caps

Best regards, CAL

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