Matt,
In my earlier response, I should also have mentioned that we underfill
BGA's before coating with a reworkable epoxy. This completely fills the air
gap underneath and helps support the BGA solder joints as well. It softens
at soldering temperature so you can remove a BGA as normal (well almost -
it needs a bit more lifting power to detatch it from the board than does a
BGA with no compounds underneath).
Underfilling is not necessary though if your product is not going to be
temperature cycled much. If your coating is thin enough to penetrate
beneath components well and is applied properly, it will protect all
surfaces well enough. If you use very thin coating, you will require
several coats to build up the necessary thickness (anywhere between about 1
mil and 5 mils), since the solids content that forms the coating is a
relatively low percentage of the native coating volume. Humiseal supplies
quite good appliation notes for the various methods of applying their
coatings.
Peter
joyce <[log in to unmask]> 22/05/2003 10:32 PM
Sent by: TechNet <[log in to unmask]>
Please respond to joyce.koo
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] Conformal Coating Application Method for BGA
Use CVD.
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of
>Gray, Matthew D HS-SNS
>Sent: Thursday, May 22, 2003 9:54 AM
>To: [log in to unmask]
>Subject: [TN] Conformal Coating Application Method for BGA
>
>
>Hello -
>
>I am requesting feedback to material and processes that have
>provided environmental performance protection for BGAs and
>other large array packages. The performance environment of
>consideration is corrosion and humidity.
>
>Can users provide particular details regarding application
>process spray (inclusion of steps used for flood/fill/etc),
>dip, other, and material that has provided a high amount of
>coverage and ability to protect electrical connections and
>components in humidity and salt fog environments. Ideally,
>these materials are below the parylene step. All feedback is
>appreciated.
>
>Regards - Matt
>
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