Thermals on SMD mechanical support?

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Hi All--

On pads used for mechanical support, as in the attached image of a USB connector, would you generally use thermals? On the one hand, it seems like adding thermals will significantly decrease the strength of the mechanical connection. On the other, it seems like the lack of thermals might cause problems in production.

Michael

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It all depends. Some SMD processes might be able to handle it without thermals. Others might not.

I suspect that your concern about strength is not warranted. I'd bet that the "peel strength" of the copper significantly exceeds what would be needed. And I think that peeling generally happens from edges rather than at the middle of a patch of copper.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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I'd suggest follow the datasheet's instructions.

Is it going in an enclosure?

You should probably consider what forces will be applied to the connector and the support it will receive not just from the pcb but the housing also. If it is just a pcb you perhaps should consider how its going to be held when the connector is inserted.

(Check those vias under the connector won't short too btw)

oddbudman

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It is common for these connectors to get ripped off the board - normally the solder breaks away. If you want something robust, then go for the original B style connectors. As for thermal reliefs, I wouldn't bother having them

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In my experience, the thermals are going to give you the best reflow soldering results. I doubt thermals or no thermals is going to change the mechanical strength of the connectors at all.

As for the connector itself, I would go with one that has board guides, which are little plastic pieces of the casing which go through holes in the PCB. These make the connector much more mechanically sound.

Assuming that is a Mini B style connector, you might want to take a look at this connector, which I have used these in a few designs without any issues: http://search.digikey.com/us/en/...

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Thanks, All!

The image above is from something that is already in production. There have been a handful of warranty returns due to the USB connector breaking off (copper delaminating). Unfortunately, this renders the board unserviceable, so I've been trying to learn as much as I can. Lessons learned so far:

  1. The "no conductive traces" area is shown as a hatched polygon in the image above. You can see a couple of notches near the front of the connector. Why the notches? It's difficult to see in the datasheet, but there are two small mechanical pads which could make a difference in the strength of the mounted connector. The lesson? Look for hard to see mechanical pads...

  2. The product works perfectly, and passed CE/FCC testing. However, none of these tests addresses the issue of, "What happens if someone pulls sideways on the connector?" For a frequently used connector, through-hole mechanical support, positioning posts, and/or support from the case are great ideas. Next time, I'll do more testing to identify issues like this before production.
As a side note, I've also learned that every unit in the field becomes a liability when a warranty issue arises. You've sold 10,000 pieces? Great! There's a small design flaw in all 10,000? Your success just became a part of the problem.

Michael

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There's a reason Apple went to those magnetic power connectors. And PC laptops should go to them no matter how much Apple charges for the rights.

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Connect a top mounting pad to a matching bottom pad with a large via.
Or, use a molecular bonder (tech-bond.net) to secure the entire connector to the PCB; but may have to manually solder the connector.

"Dare to be naïve." - Buckminster Fuller

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If I understand correctly, the molecular bonder is pretty close to the solution I've chosen.

As it turns out, Krazy Glue wicks under the part fairly well, and makes the mount stronger than the USB cable. The nice thing is, this is something people can do in the field, so the impact was relatively minor. For future production, it's easy enough to add adhesive, so I don't even need to toss the boards I've got, order a new stencil, etc.

I haven't identified a specific adhesive for new production, however. I'll definitely take a look at molecular bonders.

All in all, a pretty cheap lesson.

:D Michael

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http://www.tech-bond.net/Debonders_Accelerators_Gels.html states molecular bonders are stronger than cyanoacrylates.

"Dare to be naïve." - Buckminster Fuller

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crwper wrote:
All in all, a pretty cheap lesson.
Yep. It didn't cost me a penny! Thanks for sharing.

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia