On Jun 24,  2:53pm, Frank Hinojos wrote:
> Subject: Tented Vias
>      A couple of weeks ago I asked all of you about the dangers of
using 
>      tented LPI vias.  I received an overwhelming response that while
it is 
>      good for assembly, it may be very detrimental to the boards' 
>      reliability due to chemical interaction of contaminants and
uncured 
>      LPI in the via.  Why then does it seem that everyone is using
tented 
>      vias and why haven't we heard of problems arising due to your 
>      concerns?
>      
>      Frank Hinojos
>      Watkins-Johnson Co.  

>-- End of excerpt from Frank Hinojos

Frank,
Application, application, application.  Tented via are just fine in a
commercial application.  If it breaks, worse case, you have an upset
customer.  Few commercial companies are going to do the failure analysis
to figure out what the problem was.  Highest volume in the business is
commercial, so it seems every one is doing it.

However, if it breaks in a communications satelite, or causes a 747 to
make an emergency landing, you can bet there will be people trying to
figure out why.  One Root cause statement like "air pockets trapped by
tented vias suddenly expanding into the vacuum of high altitude,
displaced a surface mounted component creating an open circuit" is all
it takes in that small design industry to raise a major reliability
flag.  (Root cause is my pure fictional creation.)

The statement that "gee, everyone else is doing it, and they are not
having problems" is logic that I used as a teenager, and try to fight
against with my teenager.  Just because LPI tenting is OK for a
hand-held calculator, does not mean it is OK for Watkins-Johnson.  Or,
maybe it does.  Your call.

Know your risks, understand your application, make your decision.

George Franck
-- 

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************