TECHNET Archives

February 2001

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Creswick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 15 Feb 2001 20:29:13 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (111 lines)
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
---------------------------------------------------------------------------------

ATOM RSS1 RSS2