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Max temp on a lead free part


Rob

#30998

Max temp on a lead free part | 18 October, 2004

Hi Guy's,

Sorry about this, but yes it's another lead free related question.

We are looking at using a Chinese SMD DC-DC Converter in a new design, whilst keeping one eye on the approaching Lead-free issue. The manufacturer claims that these are OK for lead-free, but the max temperature (measured on the top of the component body) should not exceed 235C for more than 6 seconds. This seems a little low for me, but it's only a gut feel as I'm a lead free novice.

Any suggestions?

Cheers,

Rob.

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#31000

Max temp on a lead free part | 18 October, 2004

Rob

230C does sound low. Typicaly most lead free solders need a TAL of >45 seconds from 230-245C. Check your paste material of choice for recomended profile peak temp and TAL. If you have not selected a lead free material check out the major paste suppliers on their lead free material offering and review the specs.

thanks marc

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KEN

#31005

Max temp on a lead free part | 18 October, 2004

I have two industry leading customers that have specific requirements for components to survive 30 seconds above 230C.

In one case I have a custom ASIC that is heat sinked on the die (to the PCB). The sink pulls heat out of the lead frame very efficiently to the point I have other areas of the board hiting 263 (peak) just to get to 245 on the ASIC lead frame.

As expected component infant mortality has been the biggest issue. However, this is directly driven by the ASIC design and the customers requirement for a given themal contact patch under the ASIC. This same design was used in tin/lead, however, the peak temps were 235C which (I suspect) was in the unreported SOA of component manufacturers.

Fot the types of assemblies I see, 235C is rather low. However, we typically have 8-16 layer boards. If you have 2-4 layers you may be ok.

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Rob

#31031

Max temp on a lead free part | 20 October, 2004

Gentlemen,

Thanks for your feedback - I think we are going to have to stay with the parts we are using.

Cheers,

Rob.

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Rob

#31118

Max temp on a lead free part | 28 October, 2004

Any comments to add Dave?

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#31234

Max temp on a lead free part | 4 November, 2004

Definetely 245�C

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Rob

#31237

Max temp on a lead free part | 5 November, 2004

Thanks Mark, we're not going to go anywhere with that particular supplier now.

Cheers,

Rob.

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#31258

Max temp on a lead free part | 8 November, 2004

It's possible your supplier has not thought through the results of their conversion to lead-free throughly. We'd expect something like: Reflow Parameters||Pb Assy||Pb Free Peak Temp.||235�C �5�C||255�C �5�C Time Within 5�C Peak Temp.||20 to 40 sec.||20 to 40 sec.

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Rob

#31264

Max temp on a lead free part | 8 November, 2004

Thanks Dave,

I'm guessing they either were just hoping they'd be ok, or were suppling them to people using nitrogen.

Cheers,

Rob.

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