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Subject:
From:
Mike Bogden <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 15 Dec 2010 08:04:21 -0800
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What is the effect of a void and the trapped gases in a 0G enviroment?

Mike B




________________________________
From: Werner Engelmaier <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, December 15, 2010 7:24:13 AM
Subject: Re: [TN] X-ray inspection of voids under chip caps and resistors

Hi Phil,
It is an old story---just because you can measure something---even with, or 
maybe because of very expensive equipment, does not make it necessarily 
significant or important. It has been shown over and over again, that voids in 
the normally produced ranges have no negative [there is actually a slight 
positive effect under some limited special conditions] reliability impact. 

It is like the EU specifying the allowable curvature of bananas.
Werner 






-----Original Message-----
From: David D. Hillman <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, Dec 15, 2010 8:11 am
Subject: Re: [TN] X-ray inspection of voids under chip caps and resistors


Hi Phil - There are a number of X-ray systems on the market that can 

accomplish the task per the NASA Workmanship standards but the question 

really should be "why is there such a requirement?". Rockwell Collins, 

RIM, Indium and Dage are finishing up a BGA voiding study that shows voids 

are not a "primary" issue to solder joint integrity. We will be proposing 

to the JSTD-001 committee new BGA voiding requirements, in collaboration 

with a number of other industry investigators, at the IPC 2011 Fall 

meeting. I find it a bit hard to believe that a chip resistor needs a 

stricter solder joint void requirement than a BGA component.



Dave Hillman

Rockwell Collins

[log in to unmask]







Phil Bavaro <[log in to unmask]> 

Sent by: TechNet <[log in to unmask]>

12/14/2010 06:06 PM

Please respond to

TechNet E-Mail Forum <[log in to unmask]>; Please respond to

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To

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Subject

[TN] Xray inspection of voids under chip caps and resistors













Are any Technetters working with the newly drafted Workmanship standard

(WSF 11122010) from NASA?



I am surprised that they are intending to implement xray inspection of

voiding on chip caps and resistors.



It appears they want us to determine the percentage of voids greater

than 1 mil and then add up the areas both for the beneath component and

then the external fillets.



While I suppose it is progress to have NASA embracing water soluble

fluxes, this seems like a huge hurdle to have to cross first.







Here is the requirement as drafted:







1.      The X-ray process (including equipment, operator and procedure)

shall be capable of discerning a solder void that is one thousandth of

an inch (0.001") in diameter.  If the supplier's X-ray capability is not

adequate, specimens can be sent to GSFC for X-ray. 



2.      For each PWA or coupon examined via X-ray, five worst case

examples on the PWA or coupon shall be selected for measurement to show

compliance with the following criteria: 



a.      For parts with chip package styles (e.g. resistors, diodes,

capacitors) and for flatpacks, a minimum of 75% of the solderable area

directly under the end cap or lap portion of the lead shall be

filled/wetted (i.e., using the solderable area under the end cap or lead

as the denominator and that area less all absences of solder - voids,

areas where the solder did not wet, overhangs due to misregistration,

etc. - as the numerator).  This requirement applies only to the area

directly underneath the end cap (chip packages) and lap portion of the

lead (flatpacks), and does not apply to other package styles and does

not include any portion of the fillet. 



b.      For all package styles, the void area in the fillet area shall

include only those areas that are completely enclosed with solder, and

shall not exceed 10% of the area covered by the fillet. 







I know that some xray systems have pretty helpful software packages for

void detection, but I don't remember any that looked at solder

percentages beneath the component versus fillet versus both.













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