I posted a question about RF shields some time back but did not receive a
wealth of replies.  The shield I saw was aluminum based and was extracted
from an autopsied  cell phone.  A quantitative elemental analysis revealed
common aluminum with a 96% nickel 2% copper plating.  It was obviously
reflow soldered with no clean paste.  The shield was not staked by adhesive
or tabs and had nice solder fillets.  The shield had holes in it to
apparently allow for convection heating the components within the shielded
area.  This suggests that the components are soldered at the same time as
the shield making assembly very efficient and requiring a very stable and
characterized rf design.  I have tried to reflow solder to nickel in an RF
assembly in a previous life and found that the solderability of nickel
varied so much that I could not do it reliability, and that no clean
residues interfered with the rf path due to leakage (the residues although
dielectric to dc were permeable to rf).  Perhaps the plating with 2% copper
is a key, although it could have been trace copper underplate.  The shield
was obviously manufactured from a die stamping process.  We discussed the
soldering with our experts and they felt that the process would be aided
with a nitrogen atmosphere in the reflow process but we do not have the
resources at the facility to test rf and have no shields to experiment with.

Denis Meloche
Heraeus Cermalloy
610-825-6050

At 12:17 PM 7/11/97 +1200, you wrote:
>I was interested to see some discussion on the use of SMD shields pre
>reflow.  Is there anybody out there who has experience with the use of
>shields for RF shielding and is willing to divulge information?  I am
>interested particularly in:
>-drawn shields versus folded shields
>-thermal dynamics of shield use.
>
>Any comments much appreciated.
>
>Cheers
>Jesse 
>Tait Electronics, New Zealand
>
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