Message
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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