Rick,
My 2 cents on the subject..
If u do not require very high performance and at the same time expect
easy processibility, try the no-flow underfills. They are easier to
process (ofcourse, when implemented properly) with no painful
dispense optimisation. Dexter, Hysol.. have few in the market.
Best regards.
MURTHY. S.S.
> -----Original Message-----
> From: Creswick [SMTP:[log in to unmask]]
> Sent: Friday, February 16, 2001 9:29 AM
> To: [log in to unmask]
> Subject: Re: [TN] Flip-chip underfill?
>
> Rick,
>
> Could you provide a little more info, such as how large is device and the
> bump dia & pitch? Number I/O's?
>
> Is the flip chip bump composed of Sn63, or a IBM C4 structure?
>
> How large are the corresponding solderable pads on the PWB?
>
> How close are the nearest adjacent components?
>
> How many do you have to put together?
>
> Are you planning to co-reflow the FC with SMD's, or secondary reflow?
>
> What dispensing equipment do you have available to use?
>
> How do you plan to align and place the flip chips?
>
>
> Indium (and others) make no clean flip chip fluxes. One can either dip
> the
> solder bumps approx 1/3 to 1/2 way of their height into a paste-like flux,
> or jet or dispense a wee bit of the same flux in a very low viscosity
> version. I believe that Indium's part number designation is FC-NC-LT-A,
> B,
> C, D (where FC means Flip Chip, NC = no clean, LT=low temp (Sn63 like) and
> A
> thru D denote viscosity (A=like alcohol, D= like a paste flux).
>
> Big, oversize (or otherwise 'fat') fillets are visually unappealing, and
> (in
> my testing) less reliable than small, but uniform fillets.
>
> Most underfills that are applied after FC attachment will require the
> component to be heated to 70-90°C to enhance the capillary flow of the
> material. Post-dispense cures range from 125°C to 150°C, depending on
> supplier, etc. etc. Times range from minutes to about an hour.
>
> Rework after underfill cure is a pain, so essentially be assured that all
> is
> well before sealing it up tight with underfill.
>
> Scads of people to supply underfills - Dexter Hysol (now part of Loctite),
> Ablestik Labs, Kester, Alpha, Emerson & Cuming (Ablestik), Loctite, .....
>
> Placing the chip by hand may not be the smartest thing to do, but with a
> reasonable setup, and small die (say less than 0.100" square) you should
> be
> able to dispense by hand with something similar to an EFD dispenser.
> Underfill from two adjacent sides only - let the capillary flow bring it
> under the chip and to the other sides. For larger chips, one might be
> better to use a dispenser that you can program a path. Whatever you do,
> do
> not allow the underfill wavefront to deplete the available reservior
> (excess
> material not under the chip). If the reservior is depleted, you can pull
> air under the chip - oops!
>
> Do you plan to check for underfill voids? X-ray generally will NOT work!
> Got an acoustic microscope??
>
> What environmental requirements do you have to meet?
>
> Parting shots - If is a low rel, cheap & dirty PWB, you may get away with
> it. If it is a higher quality project, where the customer can come back
> and
> bite you - tread carefully. It may appear easier than it actually is
>
> Have fun!
>
> Steven Creswick
> CTS RF Integrated Modules
>
>
> At 10:57 AM 2/15/01 -0800, you wrote:
> >We've been asked to do a small proto run of flip-chip assemblies. I'm
> >looking for some insight on how best to underfill these parts. Is manual
> >equipment sufficient to do this? Any input as to materials & methods
> would
> >be appreciated.
> >
> >Thanks in advance,
> >
> >
> >Rick Thompson
> >Ventura Electronics Assembly
> >2655 Park Center Dr.
> >Simi Valley, CA 93065
> >
> >+1 (805) 584-9858 x-304 voice
> >+1 (805) 584-1529 fax
> >[log in to unmask]
> >
> >-------------------------------------------------------------------------
> --
> ------
> >Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> >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 delivery of Technet send the following message: SET
> Technet NOMAIL
> >Search previous postings at: www.ipc.org > On-Line Resources & Databases
> >
> E-mail Archives
> >Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> additional
> >information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> ext.5315
> >-------------------------------------------------------------------------
> --
> ------
> >
> >
>
> --------------------------------------------------------------------------
> -------
> Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
> 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 delivery of Technet send the following message: SET
> Technet NOMAIL
> Search previous postings at: www.ipc.org > On-Line Resources & Databases >
> E-mail Archives
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> additional
> information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
> ext.5315
> --------------------------------------------------------------------------
> -------
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
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 delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
