Hi Jorge
Yes there is something very wrong with those parts. We are having the
same problem. Watch them carefully under a microscope at a rework
station and you will see dielectric come out of the part. The
dielectric will float on top of the solder paste, preventing it from
wicking up the side of the leads when it reflows. If you remove the
tombstoned component, you will see the dent in the solder paste, where
component termination pressed into the paste, but didn't wet. You will
also find the dielectric still on the PCB between the pads.
Actually, those Panasonic parts are a hundred times better than their
competitor's parts which do not have a plastic encapsulate. The other
parts lost a big puddle of dielectric, and the capacitance plates melted
when touch up operators touched them with their irons.
In order to completely get rid of the "tombstones", we will experiment
with dispensing paste from a CAM/ALOT glue machine on the pad of those
capacitors. Once the paste wets the leads, it seems it displaces the
dielectric.
Thanks
Ryan Grant
Process Development Engineer
MCMS
(208) 898-1145
FAX (208) 898-2789
[log in to unmask]
>-----Original Message-----
>From: Jorge A Rodriguez [SMTP:[log in to unmask]]
>Sent: Saturday, September 04, 1999 9:03 AM
>To: [log in to unmask]
>Subject: Re: [TN] Tombstoning
>
> We are having this problem on totally different boards. So far I've
>found 5
>different boards with the same problem and the plastic film capacitors are
>the
>only components from all the boards that we have this issue. As far as the
>placement and paste deposition everything is OK. Also these parts are not
>placed too close to larger parts. I am trying to find out if somebody has
>had
>problems or similar problems with these plastic film capacitors and what
>they've
>done to solve it. Also if there is any special consideration for these parts
>different to what it's done with ceramic capacitors. I guess I can say it in
>one
>simple phrase, is there something wrong with this type of capacitor?
>
> Any suggestion.
>
>
>
>
>
>
>"Taheri, Kamran" <[log in to unmask]> on 09/03/99 03:54:38 PM
>
>Please respond to "\"TechNet E-Mail Forum.\" <[log in to unmask]>,
>\"Taheri,
> Kamran\"" <[log in to unmask]>
>
>To: [log in to unmask]
>cc: (bcc: Jorge A Rodriguez/El Paso/USA/Conexant)
>Subject: Re: [TN] Tombstoning
>
>
>
>
> Are these parts too close to any larger parts or ground plane that
>could upset the thermal balance? Is your paste deposition and part placement
>dead on? Is your paste fresh? If your answer is no to first and yes to last
>two questions, then I would suspect your profile to be the cause.
>
>> -----Original Message-----
>> From: Jorge A Rodriguez [SMTP:[log in to unmask]]
>> Sent: Friday, September 03, 1999 3:57 PM
>> To: [log in to unmask]
>> Subject: [TN] Tombstoning
>>
>> I am having a lot of tombstoning with 1206 plastic film
>> capacitors
>> (stack metallized film) part numbers ECHU1H392JB5 and ECHU1H123JB5 from
>> Panasonic. Pad design was already checked and it seems alright. From all
>> the
>> chips on the board, these are the only ones that we are having problems
>> with.
>> Also the oven profile it's OK too (we are using a Unitherm Vitronic
>> convection
>> oven and Kester 256 no clean solder paste). One think I noticed it's that
>> the
>> components seem to be lighter in weight compared to the ceramic
>> capacitors.
>> Has anyone had a similar experience? , what can I do to improve the
>> process?.
>>
>> Any comments/suggestions. Any information is appreciated.
>>
>>
>> Thanks
>>
>> Jorge Rodriguez
>> Conexant Systems
>> [log in to unmask]
>>
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