I agree that wire bonds in a cavity will weaken the bonds if the 
ultrasound frequency creates a mechanical resonance. It may be a year or 
two before the component actually fails, perhaps a shock finishing the 
job. I also agree that encapsulated dies do not fail under the same 
conditions. I've come across two other damage mechanisms:
1. glass-housed quartz crystals: the silver electrode parts company with 
the crystal round the solder joint
2. very large multilayer ceramic capacitors: where the height exceeds 
the quarter-wavelength of the ultrasound in the medium, I have seen 
cleavage across the capacitor. This was insidious because the solder web 
kept it visually and electrically intact, until a year or so later when 
the top bit of the component fell off, losing quite a large slice of 
microfarads.

Brian

On 12/10/2011 16:10, Steven Creswick wrote:
> Dave,
>
> If there were any cavity packages, such as mechanical relays, HYBRIDS,
> CPU's, crystals, etc on the board they could indeed be susceptible to
> possible mechanical damage caused by the ultrasonics.  I have observed the
> results of individuals placing SEALED hybrids [cavity style packages] into
> ultrasonic cleaners with devastating results to the wire bonds.  Placing the
> same hybrids into the ultrasonic cleaner in an un-sealed state did not
> affect the wire bonds [but prove out one's own process to be sure].
>
> Conversely, if the devices are plastic encapsulated PEMs, with no internal
> cavities, they are essentially immune from any reasonable ultrasonic
> exposure that I can imagine.
>
>     If there are cavities - tread with caution.
>     No cavity, total encapsulation - typically safe!
>
> My 10 cents
>
> Steve Creswick
>
>
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Wednesday, October 12, 2011 8:14 AM
> To: TechNet E-Mail Forum; Amol Kane
> Cc: [log in to unmask]
> Subject: Re: [TN] Wire soldering question - Utrasonics discussion
>
>
> Hi Amol - you can call it a myth or just old tribal knowledge but for many
> years there was (and still is in some segments) the idea that ultrasonics -
> either soldering or cleaning - will damage the die or the wirebonds in
> components. There are a number of good industry publish investigations that
> show ultrasonics can be applied for in both the cleaning and soldering
> applications safely without causing component damage provided you do
> sufficient process qualification. I am not a fan of ultrasonic soldering as
> I can ultrasonically solder a toothpick - the solder sticks mechanically and
> not because I made a metallurgical interface. But, ultrasonic soldering is a
> viable process provided attention is paid to making metallurgically sound
> solder joints. Ultrasonics have wide application in cleaning processes.
> Other TechNetters can provide better information on that aspect than I.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> ______________________________________________________________________
> This email has been scanned by the MessageLabs Email Security System.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 16.0
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
> -----------------------------------------------------
>

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------