Dendritic growth, also referred to as metal migration, is a formation of
metal filaments (dendrites) governed by the availability of metal, the
presence of condensed water and ionic species, and the existence of voltage
differential. The metal migration phenomenon leads to an increase in leakage
current between the bridged regions, or causes a migrative resistance short
if complete bridging occurs. Metals known to demonstrate metal migration
include lead, tin, nickel, gold, copper, and silver. The migration
phenomenon is an electrolytic process, that requires a conducting
medium-usually water-with dissolved ionic species. Ionic species include
impurities such as chlorides, bromides, or products generated during
corrosion. The driving force behind metal migration is the potential
difference that exists in a biased package. Since this phenomenon is
time-dependent, it is classified as a wearout mechanism.
Silver is one of the most widely cited materials for dendritic growth.
Silver dendrites typically grow from the bond pads through an electrolytic
process. In biased tests, Dumoulin [1982] observed that the metal from the
anodic (positively charged or higher potential) areas migrates to the
cathodic (negatively charged or lower potential) areas and forms dendrites
there.
Dumoulin, P., Seurin, J. P., and Marce, P. Metal Migrations outside the
Package During Accelerated Life Tests. IEEE Transactions on Components,
Hybrids, and Manufacturing Technology, CHMT-5, No. 4 (December 1982)
479-486.
Silver migration in conductive adhesives
Electrically conductive adhesives (ECAs) are composite materials consisting
of a dielectric curable polymer and metallic conductive particles. One of
the greatest concerns with the reliability of silver-loaded conductive
adhesives is silver-migration. In this mechanism, the silver is ionized and
migrates in a humid environment, forming electrically conductive dendrites
that can result in electrical shorts between interconnects. Silver migration
can only occur if the silver particles are directly exposed to a corrosive,
humid environment. The silver in ECA joints is encapsulated inside the
polymer, and it is difficult to promote dendrite growth from within the
joint if corrosion does occur. Work by Hvims [1995] and Rörgren and Liu
[1995] indicated that silver migration was never observed in any of the
accelerated corrosion tests performed.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Michael Forrester
Sent: Friday, February 16, 2001 5:29 PM
To: [log in to unmask]
Subject: [TN] Silver Conductive ViaPlug
Our R&D department is starting to design boards with vias in pad. The plan
is
to fill the vias with Dupont CB100 silver conductive Viaplug.
Currently the plan is to have 10 mil plugged vias under all of the BGA pads
to
simplify the design, and then Nickel/Gold plating of the pad.
My concern is that this concept started on one design and in two weeks has
spread to 16 designs and we have no history with boards
manufactured with conductive Viaplug. The new designs use HASL,
Nickel/Gold,
and OSP as surface finishes. The ViaPlug has a Tg of
115 C and a TCE of 35. The PCBs are FR4 -12 layer, and FR4 -2 layer. Has
anyone had any good or bad experiences with this
technology? What are the concerns using this technology? Thank you.
Best Regards,
Michael Forrester
LeCroy Corp.
----------------------------------------------------------------------------
-----
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
---------------------------------------------------------------------------------
|
