I am with you. I would do all four at once if I could

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Friday, June 08, 2007 4:47 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] Z-axis expansion

Hello,

Thank you for the point in the right direction !!


The reason I am asking is because we have some boards with BGA memory.
There are 4 devices on one side of the PCB in very close proximity and 4
more directly underneath the top 4.

So, in an area 5cm x 1.5cm x .5cm of this PCB I have 8 microBGAs which X
amount of them are failing because of cold solder.  Other people's wisdom is
to rework the BGAs one at a time but my concern is exposing such a small
area to lead-free temperatures up to 8 times.

I would imagine with 1 mil or 800 micron via thickness that the z-axis
stresses would be too much for 8 reflow cycles so I am trying to argue the
point of reworking (or replacing) at least 2 BGAs at a time.

Thank you,
 
David Tremmel

 
-----Mensaje original-----
De: TechNet [mailto:[log in to unmask]] En nombre de Hfjord Enviado el: Friday,
June 08, 2007 3:09 PM
Para: [log in to unmask]
Asunto: [TN] SV: [TN] Z-axis expansion

All you need is to say 'Thank you' to Tom Buck at DDI.
His paper tells you ALL about what you're asking for.

http://www.smta.org/files/SMTA_Boston_pbfree_ddi.pdf

By the way, why do you ask? 

Inge

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För David Tremmel
Skickat: den 8 juni 2007 21:13
Till: [log in to unmask]
Ämne: [TN] Z-axis expansion

Hello,

 

I have seen comments regarding z-axis expansion that boards and components
experience during reflow; would any of the gurus care to give some numbers?

 

Such as the copper in the vias has such-and-such expansion versus a High Tg
FR4 which has such-and-such z-axis expansion.  (I am sure someone is going
to correct me because I did not use the correct terms).

 

 

Thank you in advance,

 

David Tremmel

 

 

 


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