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SOT Solder Problem

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We are having solder issues with this part. (See attached p... - Aug 06, 2008 by SWAG  

#55873

SOT Solder Problem | 6 August, 2008

We are having solder issues with this part. (See attached picture). Placement is good prior to reflow. All other parts are reflowing well and oven profile matches paste mfg. specs. well. This is non-ROHS, WS process. Any ideas on what might be happening?

Attachments:

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#55876

SOT Solder Problem | 6 August, 2008

If everything else solders good it has to be the part, Test solderability, insure placement force is correct and as a last resort bake the part.

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#55881

SOT Solder Problem | 7 August, 2008

Is this part placed on first-side processing? Is this defect being detected after second-side processing?

We've had this happen before when running the second side of the board, parts being pulled, apparently, by the belt in the oven while being reflowed. We've corrected by lowering the bottom side temperature of the oven, in an attempt to prevent that side of the board from getting into reflow during second side processing.

cheers ..rob

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#55886

SOT Solder Problem | 7 August, 2008

It's a single sided board.

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#55889

SOT Solder Problem | 7 August, 2008

We agree with Doug. These parts appear to have poor solderability. It looks like during reflow the parts are sitting on top of the molten solder and the fans are blowing them off the pad.

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#55926

SOT Solder Problem | 11 August, 2008

Try using glue dots under the SOT before reflowing the parts and see if that doesnt resolve your problems.

Chris

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#55938

SOT Solder Problem | 11 August, 2008

Try tinning a few parts by hand and place them into the paste and reflow. If they solder fine then, you have a plating problem. Common sense goes a long way.....

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#55948

SOT Solder Problem | 11 August, 2008

Although its a fairly rough image to look at I'd think you more of a reflow or paste issue. Looking at the two resistors, they don't look so good either. Although they maintained their placement alignment the solder does'nt appear to have flowed correctly ,plus I see what appears to be a large blow hole. Maybe I should just clean my glasses?

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#55949

SOT Solder Problem | 12 August, 2008

Hi,

Is the footprint per the component manufacturers recommendations? The reason I ask is because it kinda looks like the pads are extending beneath the component. Could cause the part to float up on top of the solder and not allow the leads to wet properly. Maybe if you had the stencil openings shortened a bit at the center of the footprint it might help. One time I had similar problems with chip resistor networks, and shortening the openings helped me...

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#55954

SOT Solder Problem | 12 August, 2008

What is the plating of the component leed ?, looks like the component need more T�, perhaps you are using leed free component with SnPb solder paste at 220 �C.

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#56477

SOT Solder Problem | 11 September, 2008

Never did find a fool proof solution. Solderability seemed O.K. (at least using the methods we have available in house). Tinned parts and placed by hand and saw little improvement. Pad design is slightly different than recommended but likely not in a way to cause what we are seeing. Ended up (as rafa has mentioned) cranking up soak above paste mfg. typ. spec. range approx. 15 seconds (still under max.) and pushing TAL and PEAK to the very top of paste mfg. specs. Solder fillets are still questionable (in my opinion) but parts are no longer randomly shifting. Customer is happy and bought off process/solder quality. Customer admitted they have had this same component problem with the other supplier of this assy; it just might be a design thing so we'll take the easy road and blame it on the EE's.

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#56482

SOT Solder Problem | 11 September, 2008

So, you just "patched it up" until next time the same problem will pops up.

Is it what some of us call "probelm solving", or (as I'd call it) "probelm hiding"? :-)

Vlad

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#56493

SOT Solder Problem | 12 September, 2008

Are there tantalums close to these SOT's? Could be related to a previous thread on moving components in reflow oven. http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=11279&#Message46732

Steve.

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GSx

#56494

SOT Solder Problem | 12 September, 2008

Had same problem with SOT23 (two different PNs and Suplliers) problem was random (AVG 0,15%).

Parts are RoHS but soldered by SnPb, Lead frame Plating (e3)according to IPC-J-STD609 it means Sn pure (check the label on reel), additional info, it is Sn matte finish.

The time above 200�C has been increased to 45"-50". Peack a bit less then 235�C (parts are Lead Free reflow capable)

By running this profile, problem has been left.

Pls, investigate on lead frame plating.

To deal with RoHS parts, the termination plating is an important aspect to take care, soldering by Lead Free alloy or by SnPb alloy.

Best regards......GSx

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#56499

SOT Solder Problem | 12 September, 2008

When you sat design problem, is it a because there is a ground plane causing a thermal problem?

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#56500

SOT Solder Problem | 12 September, 2008

This question maybe more for myself than SWAG, but, could this be a DELTA problem caused by design? (Ground Plane)

One side of the component reflows later causing the component to twist???

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#56514

SOT Solder Problem | 15 September, 2008

Thanks all for the input. There are no tants. close to these parts. GSx - you are correct in that this is ROHS compliant component so maybe a plating issue. We have done what you describe but to a lesser peak with fair improvement. Not seeing much movement but still not an ideal solder joint. Real Chunks - yes, this is an interesting design in that there are planes in this fairly thick PCB beneath these part that could be causing problems. In addition to this, this board is shaped like a donut and the trouble parts are next to the hole in the center.

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