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Problems with Maxim TQFN 38 pin part

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Oswaldo Rey

#48380

Problems with Maxim TQFN 38 pin part | 13 March, 2007

I placed a Maxim MAX16810 38 pin TQFN with a power pad ground on the bottom of the chip on a prototype board FR4 doble sided. Vias of 0.6 mm where placed underneath part, 6 vias in total. Solder was placed with an air operated syringe, land pattern was created according to manufacturer and vias where also recommended by manufacturer.

I placed part on pcb, hand assembled but reflowed, the part apparently flew of pc board and landed upside down very near its land pattern, I think that hot air from vias probably pushed part upwards.

I have assembled many similar parts but this had never happened, I also don�t know if this could of happened because vias are 0.6mm diameter. Maxim recommended 0.4mm vias.

Although part is not easy to hand place, its a prototype and in production it will be machine placed, but the problem was during reflow.

I tried a second time with vias filled with solder and part didn�t fly off but was shifted sideways and skewed, far from being acceptable. Maxim doesn�t specify how much solder should be placed on power pad, on some parts its 50%, I placed close to 100% because of vias being filled and supposedly should draw out the hot air, but hot air goes up, not down...

Any previous experiencie with this part ??

Thanks,

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#48382

Problems with Maxim TQFN 38 pin part | 13 March, 2007

Hi,

We solder a part almost identical to this without problems. Could it be your airflow in your oven is set to high?

On our prototypes we didn't place any solder on the middle bad as it was not a connection, and we did not need it thermally, however you could put only enough for contact, but you need to know if your going to have a thermal issue.

Regards,

Grant

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Oswaldo Rey

#48395

Problems with Maxim TQFN 38 pin part | 14 March, 2007

There is an approximate 1W dissipation and has a 2 sq in area below part on solder side as a heat sink, vias are to physically conect this solder side area to power pad, so its necessary to use an adequate amount of paste. I really don�t think it has to do with amount of air, since other smaller parts do not blow off, on the initial test, part seemed to "blow" upwards and landed upside down on its same land pattern which makes me believe it was pushed upward with certain force. Since part has pins an all 4 sides, there is no other way to connect ground plane if not with vias...

thanks,

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Hussman

#48397

Problems with Maxim TQFN 38 pin part | 14 March, 2007

Are these blind vias or do they go all the way thru the board?

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Oswaldo Rey

#48398

Problems with Maxim TQFN 38 pin part | 14 March, 2007

Vias are thru hole, pcb is two sided, bottom copper is 2 sq inches, vias are 0.6mm diameter. thanks,

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#48447

Problems with Maxim TQFN 38 pin part | 16 March, 2007

A quick experiment idea: Try reflowing a bare board prior to assembly. Perhaps your boards have moisture and outgassing issues.

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Oswaldo Rey

#48566

Problems with Maxim TQFN 38 pin part | 22 March, 2007

Good idea, I�ll try this, thanks.

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