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SOT23 jumping off pads when reflowing

James

#25735

SOT23 jumping off pads when reflowing | 16 September, 2003

I am having a problem with SOT23 moving off their pads during reflow. We did not have this problem yesterday. On the pads and surrounding area looks like a lot of flux spatter. I looked through the threads but they didnt help me much. I know what 3 factors it could be:

Time and Temp? Moisture in the parts? Outgassing of the PCB?

I am not quite sure where to start first. The profile seems to be in SPEC and since we did not have this problem yesterday I would assume the profile is correct. Any ideas would be greatly appreciated.

Thanks

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mantis

#25737

SOT23 jumping off pads when reflowing | 16 September, 2003

James, Could it be the convection in the reflow oven itself.Maybe somebody has increased the air flow or convection rate. I have seen an issue with an sot23 blowing off pad in a BTU paragon due to air flow in air curtains being too high.

Hope this helps

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Gabriele

#25738

SOT23 jumping off pads when reflowing | 16 September, 2003

Hi James, is it your oven a convection forced air ? if yes you should check if air flow speed is too high.

Also, some time ( do not smile pls !!) it could be a metter of magnectic field inside oven tunnel. The SOT leads are normally madeby A-42, an ironmagnectic alloy that could be effected by magnectif fields available inside oven (generated by IR wave). But if you never had this problem in the past, i think this is not the cause, unless you have changed the SOT Supplier.

Regards......Gabe

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James

#25739

SOT23 jumping off pads when reflowing | 16 September, 2003

We do have a convection oven and no one has messed with it. I am the only one who can change anything. I have it set at Medium right now on a conceptronics oven. Could this be too high? We have not had problems in the past with parts moving off of their pads....

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mantis

#25740

SOT23 jumping off pads when reflowing | 16 September, 2003

Medium should be fine,is it only one particular reference designator all the time or is it sot23's in general that are moving.Also If it is only one ref designator what are the surrounding parts and how close are they.

Gabriele, Could i have your email so that i can run something by you.It refers to the magnetic effect in reflow ovens,you sound like you have had some experience and i would love your opinion. Regards,

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James

#25741

SOT23 jumping off pads when reflowing | 16 September, 2003

It is one reference designator by a Tant C cap. When I look at the board you can see some splattering around the part. I will send you my email shortly.

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James

#25742

SOT23 jumping off pads when reflowing | 16 September, 2003

For some reason I cant claim your email to send you mine. I am registered, so I dont know what the problem is. But anyway any ideas on the last comment above?

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Gabriele

#25743

SOT23 jumping off pads when reflowing | 16 September, 2003

Also most of Tantalum Caps are iron-magnetic material made, for sure is not this case but always wen we met problems like James met, we had always sot-23, light capacitors 0603 as you know some of them have Nikel barriel (also magnectic sensitive) and Tantalumn C (magnetic) and no problems with small chip Resistors 0603 or non magnetic Tantalum caps sorrounding the obove mentionned components(??!) Could it be magic ? Regards...gbariele PS: sorry for my poor english !!

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Stephen

#25749

SOT23 jumping off pads when reflowing | 16 September, 2003

How consistant is it? If it is every board try sending one through without the Tant. Don't overlook the possibility that the tant could be the source of the problem.

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iman

#25750

SOT23 jumping off pads when reflowing | 16 September, 2003

interesting!

I recently invested a small personal fortune into books nad other related literature to boost my understanding the scientific properties of materials used in electronics and interconnection packages.

One area( one of many areas) of particular notice was the linked implications of electrical resistivity, magnetism, and semi-conductor capabilities. It comes as exciting for me to actually read this thread as I was wondering *aloud* many times to myself where would I get to experience magnetism effects, and garner my team mates' interest in this subject, within a SMT Line?

looks like we have a potential winner! keep the wonders coming!

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Daan Terstegge

#25751

SOT23 jumping off pads when reflowing | 17 September, 2003

Are there via's underneath the Tantalum, closed with soldermask on the other boardside only ? I've had a situation recently where a chip resistor was blown away by the outgassing of via's under a Tantalum. The presence of the Tantalum caused the vapours from the via's to go sideways, with such a force that it blew the chip resistor away. Still don't know what caused the outgassing (boards were baked) but I'm pretty sure that this is what caused my problem, and like you I had it with one batch only.

Daan Terstegge http://www.smtinfo.net

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#25755

SOT23 jumping off pads when reflowing | 17 September, 2003

Check the tant cap for outgassing, tant caps are notorious for breaking wind and moving parts. Try baking the caps.

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Gabriele

#25764

SOT23 jumping off pads when reflowing | 18 September, 2003

Hi all, by reading along those thread (SOT23) and Tan outgassing I learned plenty of things. My first time approacing this kind of Q$A Forum, very intesting tech communication way. Any way, the path of magnetism effect was chosen when time ago we met a problem of Tants, C-R chips jumping away or simply skewing away from their pcb locations. Yes we had a Vendor A Tantalum cap generating this pbm, we replaced with a Vendor B Tant same P/N and the problem disappeared completely. By doing a claim for Tant we discovered the Vendor A had terminal lead A-42 made (magnetic sensitive)the Vendor B had terminal lead Copper made. It was may be a case but also the other smallest Chips effected had nikel barrier on solder terminals ( if try by a magnetic tip, the chips get attracted by the tip).That's why we though about some magnetic effect inside reflow oven (IR short wave??). Unfortunately the product is no longer assembled so not possible to make further trials and test.

But after reading notes from James, Dave, mantis, etc, I am thinkig mainly to Tant outgassing effects. In fact, olong last year, we found several Tant Vendors that deliver Tants pakaged in dry -pack, inside Moisture Barrier Bag, classifing the MSL:2a (!!!), one PN MSL:3. In my opinion they are hunting for solutions against electrical value leakage but also against outgassing effect mentioned along the threads. We will keep under control the pbm during next board assembly when using same Tant P/N and by following some suggestion learned from this forum. Tnks Ciao....Gabriele

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James

#25765

SOT23 jumping off pads when reflowing | 19 September, 2003

Thanks to everyone for replys. I have to agree. I will have to watch more closely when we build these boards again. Interesting facts.................

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