http://www.johansondielectrics.com/technicalnotes/sma/JDI_App-Notes_07-0
3.pdf
Be careful....
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of John Maxwell
>Sent: Thursday, September 04, 2003 12:14 PM
>To: [log in to unmask]
>Subject: Re: [TN] Preheat of ceramic chip capacitors
>
>
>Hi Daan,
>Preheat rates is one of the most confusing guidelines ever
>stated by MLCC
>vendors. If you ask them specifically where the numbers come
>from,,, well
>don't be surprised by the answers. Basically those guidelines
>are vapor (or
>perhaps vapour) especially when you consider that billions are wave
>soldered each year and exposed to rates of change exceeding
>100C/sec with
>no cracking. I would look first at board handling for 0805
>sized chips and
>possibly fillet size and cooling rates. If parts were larger
>cooling rates
>become more important. For those that want to rush to point
>out in some of
>my much earlier publications that I repeated the party line of
>4C/sec, it
>was just that, a party line.
>
>Basically you can't crack 0805 sized MLC capacitors during
>reflow during
>the heating stage. Cool down is not very likely unless you are using
>hurricane cooling fans and huge bulbous solder joints.
>
>John Maxwell
>
>At 05:32 PM 9/4/2003 +0200, you wrote:
>>Hi Technet,
>>
>>I just saw a specification for the soldering profile for a simple
>>0805-sized ceramic chipcapacitor. It mentions a maximum preheat ramp,
>>both for wave and for reflow soldering, of 2 degrees Celcius per
>>second.
>>
>>In the beginning of the slope, for some of our products, we
>go slightly
>>higher than this. One of our customers now thinks that the
>preheat ramp
>>being steeper than the component suppliers specification must be the
>>reason for malfunctioning of this specific part.
>>
>>I won't annoy you with all the discussions we had and the
>>investigations that we've done, I just hope to get an answer to the
>>following question: is it possible that a preheat ramp of 3 °C/s
>>results in failures (but without any visible damage) of 0805 ceramic
>>chipcapacitors ?
>>
>>Best regards,
>>
>>Daan Terstegge
>>Thales Communications
>>Unclassified mail
>>Personal Website: http://www.smtinfo.net
>>
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