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Damaged Components by Reflow Process (Process Window)

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#57980

Damaged Components by Reflow Process (Process Window) | 4 February, 2009

Hi All Reflow Gurus

I have learnt that my process engineers do not consider the heat resistance, of the components when creating a reflow profile but rather try to stick to the paste recommendation. This has lead to a field recall as one component has been reflowed outside its process window and subsequently destroyed. As I investigated they told me that such data as recommended process window is rarely available from the component manufacturer. This presents a very serious problem from a liability point of view as I can not be sure now if other products reflowed may have issues as well. How can we address this matter so to ensure every board i.e. component assembled are soldered within the right process window from a component point of view?

I appreciate creative inputs. Thank you All Smartasp

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#57990

Damaged Components by Reflow Process (Process Window) | 4 February, 2009

Hi

First of all you have to respect the dwell time and the time after the reflow at peak tmeperature.(225�C for Pb and 235�C for Pbf) You can find the reflow profile from manufacturer for majority of parts designed for reflow sodlering. In general the electronic components are manufactured to withstand the temperatures given above with +/- 10�C. That is why proper reflow profile setup is necessary before starting a product and that is the key to prove the reliability of soldered parts. If you still find parts melting then it is adviceable to do a DFM on the PCB design. By the way verify & ensure that the reflow oven is working fine, might be that the temperature is something else in the zones than it shows on the display :-( Good luck...

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#57991

Damaged Components by Reflow Process (Process Window) | 4 February, 2009

You need to profile to the paste. And if a part can't take the temperatures, then you have to have something done about the parts.

At one time most components had peak temperature information back when we didn't really need it becuase profiles were cooler and components could take higher temperatures.

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#57994

Damaged Components by Reflow Process (Process Window) | 4 February, 2009

As was stated before, you need to have oven temperatures (profile) set such that you get good solder joints with the paste you are using. And definately run a profiler through yor oven to verify it is working properly.

As for components, most data sheets have a soldering specification usually listed as a maximum temperature for a cetain length of time. If the component can not handle the max temperature of your profile, you will need to design in a different component that can handle it.

Don't assume all ROHS compliant components can handle a lead free profile. While most ICs, Rs, Ls and Cs have max temp ratings of 250-260C for a few seconds, I just had a ROHS capacitor with a max temperature of 235C. With peak temps in a lead free profile in the 235-240C range, this capacitor may be damaged.

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#58000

Damaged Components by Reflow Process (Process Window) | 4 February, 2009

What do you suggest doing if you are a CM and the customer AVL/BOM tell you to use that component?...

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PR

#58001

Damaged Components by Reflow Process (Process Window) | 4 February, 2009

Hand solder it afterwards

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#58006

Damaged Components by Reflow Process (Process Window) | 5 February, 2009

The problem expressed by you need not necessarily be caused by the Reflow process even though it's effect cannot be ruled out. I suggest to validate periodically the Reflow Oven performance as also optimise Reflow parameters through a documented validation process. I hope you have already considered the possibility of component failure due to poor handling and storage pertaining to ESD and Moisture sensitivity. These have serious impact on component performance in the long run.

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#58010

Damaged Components by Reflow Process (Process Window) | 5 February, 2009

Smartasp,

Certain software packages used with Reflow Profilers have a tab where individual TC's can be set to a different spec. This will allow you to monitor package temps while still monitoring the solder paste specifications. You can define each TC with several parameters.

Goto: http://www.kicthermal.com and download their KIC 2000 software. It's free to download, but only works with their profilers.

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#58011

Damaged Components by Reflow Process (Process Window) | 5 February, 2009

could you elaborate on the type of component involved to help us understand the issue better....if this assembly is a special case you might try vapor phase soldering of that assembly...although that is a capital investment if you are not currently so equipped...

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#58032

Damaged Components by Reflow Process (Process Window) | 9 February, 2009

Bingo.

Or, work with the product designers to incorporate component processing temperature limits into their product specifications. After all, they ARE the ones that generate the BOM, right?

Yeah, I know....good luck with that.

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#58051

Damaged Components by Reflow Process (Process Window) | 10 February, 2009

Smartasp,

Seems this issue is certainly making a long thread !

As far as our Experience is concerned on Reflow Soldering, particular parts must have failed in LSLs [Lower Specification Limit] and have not withstand well under USLs [Upper Specification Limit] of Temperature & Time Graphs.

As there are none of the other parts affected in Your Circuit Assembly other than this part with same Reflow Oven & Thermal Profile, You shall talk to Part Manufacturer on the Part Temperature & Time withstanding acknowledgements.

Also ensure equalized Temperature distribution across Circuit at Cold Joints & Hot Joints as well.

And this also seems that it may not due from improper measures of ESD, Storage or Handling.

Tnx, David.

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#58060

Damaged Components by Reflow Process (Process Window) | 10 February, 2009

Dear ALL

Thanks for the valuable input so far.

The solder results is the first priority whereby the solder paste requirements sets the guidelines for the profile first. We use Kick profiler with the latest software. We verify the oven temp and distribution of the temp every day.

We did assume that all rohs components can handle the required temperatures but where wrong there. Many components have no data sheets, which inform about the reflow profile available.

Dot he comp. manufacturers have to produce to a standard and therefore not publish such information as they are working according to these? If so what are these standards?

We are an EMS company with 1300 different products to make and have now to research all the BOM's for components with temp requirements other than the standard.

By the way all MSL components are controlled, stored etc. according to the guidelines.

Thanks

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#58062

Damaged Components by Reflow Process (Process Window) | 11 February, 2009

Smart,

There must be an in-house system at Your end that any Parts intended to buy must undergone for Validation Phase in Qualification Process. At this phase Qualification Engineers to be acknowledge that each parts are meeting given TDS Specifications & no non-sense !

Though You are an EMS firm & the Parts Qualification & Procurement must be done by Customer, reach their Engineering Team to narrow down the issue. If the procurement part has been passed over to Your end, call & talk to Supplier for Assistance or Corrective Actions.

Tnx, David.

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#58088

Damaged Components by Reflow Process (Process Window) | 14 February, 2009

Thank you all for your valuable inputs.

Have having done some more investigation we have realized that there is actually no standard as such to which the ROHS components have to be manufactured aside from the contains of substances like PB and al other restricted chemicals etc..

No defined and standardized templates are available which can be used by all the electronic component manufacturers to publicize process parameters such as for example reflow temperatures ideally including the relevant profile and parameters etc..

Some component manufacturer actually do have this information readily available but as said all are doing it different. A web based database available for example to all IPC members could be a good option. Manufacturers could place their data as well as maintaining them individually.

The above is based only on what he have found out so far. In the mean time we are on the search for more practical ways, information standards etc..

Let me know if we miss something.

Cheers

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