Yes.  BGA and fine pitch work well on flex assy.  In fact the natural
flexural properties of the flex material allow for less stress on the
solder joints due to TCE mismatch, provided you don't introduce a lot of
physical 'bending' of that portion of the flex itself.  You can prevent
bending of the material directly beneath these components by having a
stiffener laminated into the substrate.
If this is a static application of a flex circuit (like interposer layer
in a CSP, or laminated to aluminum for heatsinking & rigidity), that
becomes a non issue.  However, if this device is mounted on a dynamic
flexing situation, such as a printer head, you'll definitely need a
stiffener, more robust as package size, number of joints and weight
increase.  I like placing BGA's on flex.  With a bright light, you can
flip it over and kind of 'look up its skirt' after is soldered on.  With
good process controls this is a relatively trouble free application.

Russ Steiner
TotalEMS LLC

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Don_well
Sent: Wednesday, April 16, 2003 9:21 PM
To: [log in to unmask]
Subject: [TN] Flex Board Assembly


Hello All
    Does anyone have experiences on flex board assembly.Could you please
tell me wether fine pitch SMDs and BGA/CSPs to be mounted on a flex
board?
    Any words is appreciated.

B.regards
Don
Huawei Manufacturing Technology Center
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