TECHNET Archives

May 2015

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Wayne Thayer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wayne Thayer <[log in to unmask]>
Date:
Tue, 12 May 2015 14:50:22 +0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (52 lines)
Enrico-

 

Ah, but the voids are often not spheres and the XRAY is not black & white!
So your equation would need to also include comparative densities (contrast
ratios) between the void and adjacent non-void regimes. Add to this that
there is stuff internal to the board and on the opposite side of the board,
and estimating area is about all you can do, unless you get a highly
detailed CT scan!

 

Typically, people bring up practical problems in this forum. Is this a
practical problem? Can you share some snapshots of how the IPC guidelines
are either too permissive or too conservative in certain situations?
Basically, the IPC guidelines are in place to establish relatively
easy-to-measure characteristics to serve as a basis for civilized discussion
amongst the various stakeholders for an electronic assembly. Presently, the
area of voiding is the standard we're using. Lots of software packages do an
automated calculation of this, and I'm not aware of practical problems with
the results. Zero voids as measured with an XRAY does not mean there's
actual contact being made, so it's not a perfect measurement. You can still
have "head-in-pillow", "champagne voids" too small to be picked up on the
XRAY, brittle intermetallics, etc., which will either prevent connection
entirely or substantially reduce useful life. But your suggested changes
won't help with any of these.

 

Wayne

 

From: Enrico Galbiati [mailto:[log in to unmask]] 
Sent: Tuesday, May 12, 2015 10:12 AM
To: TechNet E-Mail Forum; Wayne Thayer
Subject: Re: [TN] Voiding evaluation

 

If you are considering the missing mass (and I agree on it), the volume of
the voids is more appropriate. 

Also the evaluation of the volume of the voids can be done easily with the
X-rays: you just sum the void diameters raised to power 3 (instead of power
2 as in case of the evaluation of the area) and divide the result by the
solder joint diameter raised to power 3 too.

So the evaluation of the volume is not more complicated than the evaluation
of the area. 

ATOM RSS1 RSS2