Hi both and all,
I've saved an old but good report 'Parameters important for surface mount applications of multilayer ceramic capacitors' by Bharat S. Rawal and John Maxwell, AVX Corp. Cut from the report: " For wave soldering, large fillets are easy to inspect but they DRAMATICALLY reduce solder joint life and make the whole assembly more susceptible to handling damage. It is essential that pad sizes with known high yields are used". And the report describes how one should use high and meagre solder joints, rather than the commonly seen low and fat ones. Then, that's the way too meet LF.
I'm satified with the answers, and will adress the observandum to our CAD guys.
Thanks
Ingemar Hernefjord
Ericsson Microwave Systems
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Tempea, Ioan
Sent: den 13 juni 2005 23:31
To: [log in to unmask]
Subject: Re: [TN] Ceramic MLCs and Leadfree, John Maxwell case?
Hi Werner,
if I got it right, one should design the landpattern the same size as the chip? That is for a 1206, the landpattern should be 120 mils overall length and 60 mils wide.
Then, I am wondering how can one inspect the workmanship, not to mention eventual rework?
And secondly, how could one control the height of the solder joint?
Regards,
Ioan
> -----Original Message-----
> From: TechNet [SMTP:[log in to unmask]] On Behalf Of Werner Engelmaier
> Sent: Monday, June 13, 2005 5:15 PM
> To: [log in to unmask]
> Subject: Re: [TN] Ceramic MLCs and Leadfree, John Maxwell case?
>
> Hi John,
> LF-solder are stronger, less ductile, and creep slower--all of these add up
> to higher stresses in LF-SJs; ergo higher flex crack sensitivity.
> For chip components I suggest getting rid of the fillets--they cause
> component cracking, increasing the solder joint height under CCs and CRs, and reflow
> soldering them.
>
> Werner Engelmaier
>
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