Steven
Your view requires some qualification, IMHO. The potential cause of most
semiconductor damage by ultrasonics is resonance of bonding wires to the
ultrasound frequency spectrum. If you have analysed the waveforms, you
will understand that these depend on the transducer type, its position
in the cleaner, the speed of collapse of the cavitation etc. Generally
speaking, you will find a Gaussian distribution curve around the
fundamental frequency (result of noise) and a whole host of harmonics,
the odd ones having more energy than the even ones. There are gaps in
the frequency spectrum below the fundamental and notably between the
fundamental and the second harmonic. If these gaps correspond to the
resonant frequency of the bonding wires, no harm will result.
If the frequency is swept, then you are sure to hit resonance, possibly
several times with each sweep, but you are reducing the time the wires
will vibrate in each cycle, so that the destruction-causing energy is
reduced during a cleaning cycle, compared to a fixed frequency device
where you are unlucky enough to hit resonance.
A Japanese patent suggests that three (or more) fixed frequency
transducers, each with one-third (or less) energy, but with frequencies
with no mathematical relationship (e.g., 29 kHz, 40 kHz and 51 kHz) will
never cause sufficient resonance to cause damage, but will clean very
effectively. I understand this technique is reasonably effective.
There is another point to consider. Because of reflections from the
walls, many cleaners have interference standing waves in the solvent. If
this happens (and it frequently does), you will have small zones with
almost no ultrasound and others with almost double the energy at a given
frequency. The risk of resonance obviously will vary if your component
is at a high node or a low one.
Life isn't always that simple!
Brian
On 13/10/2011 15:42, Steven Creswick wrote:
> Richard,
>
> I do not wish to appear that I disagree with you and Dave. Yes, cavity
> packages can be safely cleaned with the right equipment and the right
> process.
>
> I also happen to feel that Crest makes about the best equipment out there,
> but not everyone has sweep frequency equipment in their shop.
>
> It appears that some individuals have 'tunnel vision' with respect to
> reading articles on ultrasonic cleaning and simply see, "IT IS SAFE TO
> ULTRASONICALLY CLEAN CAVITY PACKAGES", and then go place their parts in an
> old, fixed-frequency ultrasonic cleaner, only to then find their parts don't
> work afterwards... dah!
>
> In a general conversation, I always treat cavity packages in the context of,
> "You need to do your homework first!"
>
> PEMs are black and white on this issue.
>
> Final ten cents :-)
>
> Steve C
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Wednesday, October 12, 2011 10:06 AM
> To: [log in to unmask]
> Subject: Re: [TN] Wire soldering question - Utrasonics discussion
>
> I totally agree with Dave. Ultrasonics CAN be used safely, both for
> soldering and for cleaning, provided you use equipment from electronic-savvy
> vendors who understand the cavitation mechanics and can set the frequency in
> such a way as to be somewhat non-resonant.
>
> Crest Ultrasonics
> http://www.crest-ultrasonics.com/aqueous-industrial-cleaning-systems.html is
> one such vendor. They manufacture US cleaning systems just for electronics,
> and there is little or no danger of damage to wirebond components. If you
> have questions regarding this, ask Dr. Sami Awad at Crest. Nobody knows more
> about the subject than Dr. Awad. I do not have any monetary interest in
> Crest, just some very, very good experience with their products.
>
> Again, echoing Dave's words, you need to qualify the process.
>
> There are also ultrasonic solder pots and ultrasonic solder stations. I have
> a client who actually "solders" copper wire to glass using an ultrasonic
> soldering process that I set up for them. No intermetallic formation occurs
> with the glass, but a really good mechanical/electrical bond does occur,
> using solder as the bonding medium.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Wednesday, October 12, 2011 7:14 AM
> To: [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]
>
>
>
>
> Amol Kane<[log in to unmask]>
> Sent by: TechNet<[log in to unmask]>
> 10/12/2011 06:29 AM
> Please respond to
> TechNet E-Mail Forum<[log in to unmask]>; Please respond to
> Amol Kane<[log in to unmask]>
>
>
> To
> <[log in to unmask]>
> cc
>
> Subject
> Re: [TN] Wire soldering question
>
>
>
>
>
>
> Inge, this method would only be suitable for tinning wires... yes?
>
> Or is this fair game for leads of active components since only the leads
> are inserted in the solder pot (unlike an ultrasonic stencil cleaner for
> cleaning misprinted boards with one side populated where the entire
> assembly is exposed to ultrasonic energy?)
>
> Thanks!
>
>
> Amol Kane | Process Engineer
> Catalyst Manufacturing Services, Inc.
> 941 Route 38, Owego NY 13827
> Phone: (607) 687-7669 Extn 349 | Website: www.catalystems.com
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Wednesday, October 12, 2011 6:27 AM
> To: [log in to unmask]
> Subject: Re: [TN] Wire soldering question
>
> Keith,
>
> soldering to Nickel is not difficult. Soldering to Nickel oxide is
> difficult. There is the solution to your problem: removal of oxide.
>
> I had exactly same problem as you many years back. I solved the problem
> by
> dipping the dismantled end of the wires in a ultrasonic solder pot. You
> need
> just a small one. I demonstrated the efficiency of that method by picking
> som old and dirty nickel coins from my pocket and dip them directly
> without
> any cleaning. People marvelled by the good solder wetting. How come? The
> ultrasonic shock waves break the oxides and expose fresh nickel.
>
> Example on a small U/S soldering pot:
> http://www.advancedsonics.com/newpage5%20USP.htm
>
> My two nickels
>
> Inge
>
>
> ----- Original Message -----
> From: "Keith Calhoun"<[log in to unmask]>
> To:<[log in to unmask]>
> Sent: Tuesday, October 11, 2011 9:55 PM
> Subject: [TN] Wire soldering question
>
>
>
> We are building a small assembly for one of our customers using
> M22759/12-24 wires, (nickel plated copper, Teflon insulated). We are
> using Multicore HMP solder, (Sn5, Pb93.5, Ag1.5) for this assembly.
>
> Do any of you have a recommendation for a flux that may help in getting
> this wire to wet? The other solder joints are acceptable, we just can't
> get the wire to wet. I know that I am trying something difficult, as
> soldering to nickel is difficult at best. I would be most greatful for
> any suggestions that anyone has for this.
>
> Thanks for the excellent resource!
>
> Keith S. Calhoun
> Manufacturing Engineering Manager
> SoPark Corporation
> 3300 South Park Avenue
> Buffalo. New York 14218
> Phone: 716-822-0434 ext. 237
> Fax: 716-822-5062
> [log in to unmask]
> Thank you for helping SoPark reach our 30th year as a Premier
> Electronics Manufacturing Service Provider!
> ISO 9001:2008& AS9100B Certified
>
>
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