Let us return down to earth.
If the BGA( or any other component )failed during electrical test or if it is a dummy,
or if it is on a test board, you have all the time in the world to check it and do with
it whatever you please. This is the case when the BGA was isolated as the sure culprit
for the failure.
If you get a board which failed "presumably" because of the BGA, you are in the dark,
and limiting yourself to a few seconds is frustrating.
Maybe a few seconds are enough for missing balls or shorts. Opens are harder to find,
and cracks almost impossible.
Frustrations are very common during X-ray inspection.
Sometimes you check thoroughly the joints, only to discover later. that a bonding wire
burned. But again, if this is the case , no harm is done because the component failed
anyway.
Our long discussion should focus on why and how to check presumably good assemblies
that passed the electrical test, by  X-ray. Also, whoever is able to bring forward
information and food for thought, please do it.
Undoubtedly, for failure analysis it is one of the best tools.
Thank you,
Gaby

joyce wrote:

> the time is a fact for X-ray inspection.  If you set the contrast, tilting
> angle correctly (provide you did enough cross section to know the few type
> of failure mode: e.g. smaller balls, shorts, missing one, etc.) you can use
> only few second to inspect using X-ray (if you are really good, fraction of
> a sec.).  A lot of "leg work" has to be done prior to set up inspection in
> order to minimize the exposure time.  (use dummy parts to figure it out
> 1st...take few photo as bench mark example to train the operator, etc..it is
> a massive undertaking)...
>                               jk
> At 12:59 PM 6/2/00 EDT, you wrote:
> >In a message dated 06/02/2000 10:52:38 AM Central Daylight Time,
> >[log in to unmask] writes:
> >
> ><<  I am using an equipment of max. 160 kV and until now I was very happy
> >with it, inviting my friends to test BGA's with metal covers , their
> >equipment being too weak.
> >I don't know if we should be happy or not having this discussion, but I have
> >a bad
> >feeling. If there is something we don't know, research should be done. >>
> >
> >Hi Gaby!
> >
> >I've been searching to try and find something that talks specifically about
> >possible damage from x-ray inspection and as Paul said; I'm hitting a silent
> >wall. However, there's tons of information about radiation damage to
> >electronics in space. From reading some of it, there's no question that x-ray
> >radiation can degrade and damage electronic components. The question is how
> >much radiation does it take to damage something. I don't have the kind of
> >knowledge to know that...maybe somebody on the list that's a lot smarter than
> >me knows?
> >
> >Below is a paste from a web page of an organiztion that's been studying the
> >effect of radiation on solar panels. I think there's a few good statements in
> >there that illustrate we should be a little concerned when using higher
> >powered x-ray equipment.
> >
> >-Steve Gregory-
> >
> >Radiation effects
> >
> >The behaviour of solar cells in a radiation environment can be described in
> >terms of the changes in the engineering output parameters of the devices.
> >This approach limits the understanding of the physical changes which occur in
> >the device. Since other environmental factors may need consideration, an
> >understanding of a physical model provides a basis for estimates of the
> >behaviour in a complex environment. In addition, solar arrays of the future
> >will become more complex and may utilise materials which are affected by
> >different aspects of radiation damage. For these reasons, one should be aware
> >of the process by which radiation interacts with matter, and understand the
> >physical models which describe the processes.
> >
> >Ionisation
> >
> >Ionisation occurs when orbital electrons are removed from an atom or molecule
> >in gases, liquids, or solids. The measure of the intensity of ionising
> >radiation is the roentgen. This unit is defined by a charge generation of
> >2.58x10 -4 C/kg of air. The measure of the absorbed dose in any material of
> >interest is usually defined in terms of absorbed energy per unit mass. The
> >accepted unit of absorbed dose is the rad (100 erg/g or 0.01 J/kg). The SI
> >unit of absorbed dose is the Gray (Gy), defined to be 1 J/kg. Through the use
> >of the concept of absorbed dose, various radiation exposures can be reduced
> >to absorbed dose units which reflect the degree of ionisation damage in the
> >material of interest. This concept can be applied to electron, gamma, and
> >X-ray radiation of all energies.
> >
> >The use of silicon dioxide as a surface passivation coating and dielectric
> >material in silicon devices results in a wide range of ionisation related
> >radiation effects. The development of trapped charges in the silicon dioxides
> >can cause increased leakage currents, decreased gain, and surface channel
> >development in bipolar transistors and increased threshold voltages in MOS
> >field effect transistors (MOSFETs). Ionising radiation in silicon excites the
> >electrons of the valence band to the conduction band, creating electron-hole
> >pairs in much the same way that carrier pairs are generated by visible light.
> >
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