Neat idea the shrinks (feelin' for one too), Brian ,
that's why i saw the cleaning as overburdening the (mass) process :
share yours on metal loaded polymers : just did not live in cycling at all,
explored the Z axis conductive films (good for trials), no go,
so i'd agree something simple 's overdue .
Talking clean: insulating pull epoxies, in uBGA's pitches with gold balls on
gold pads,
to keep the epoxy off pads (or relying on 100% squeeze out [= "perfectly
clean"]?) would be a challenge .
Should work sufficiently , considering
I know you can jet out impossible (like Inge's needles); but in mass
production this is an expensive way to go,
(a lot of lemmies squeezed down the gap) .
paul
ps
one off stints 200 k's off Jakarta hey ? , with camera rolling (machete
proof west, riot helmet, ...),
yo' braver man than me mate (prefer my odds with sharks)
-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Tuesday, 4 January 2000 19:39
To: Paul Klasek; Technet
Subject: Re: [TN] Harsh Environments?
Paul
A 0,5 mm space below the 50 mm BGA is easy-peasy, lemon squeezy, given the
right
equipment, materials and sufficient time for the process. It's when the
space
gets down to less than 0,1 mm that I start worrying, such as LCCCs with a
mass
of flux residues underneath, for them to slowly exude onto the solder
joints.
I agree with you that "no-clean" is fine under the right conditions. But I
challenge you to achieve long-term reliability in Anil's exterior climate
(or in
Darwin, nearer home for you) with an 800 or so pin-out micro-BGA on an HDIS
circuit with a "no-clean" flux and voltage gradients well into the hundreds
of
V/mm. I have had personal experience of portable equipment
(semi-professional
digital video camera costing several thousand USD) failing during a one-off
occasion in Indonesia because of the inconsiderate use of "no-clean" flux -
and
I was not pleased as I had travelled 200 km from Jakarta especially to film
the
event. Apparently, I was not alone, as this manufacturer is now cleaning his
top-end equipment, although he is still using "no-clean" on his consumer
camcorders (which, being smaller, with tighter boards, probably require
cleaning, but that's another story!).
For micro-BGA circuits and similar, I forecast that the days of soldering
are
approaching the end, partially because of this and especially because of
lead-free soldering being imposed. I don't think conductive adhesives are
the
answer, either, especially anisotropic ones. The crystal ball I have
interfaced
into my computer tells me that we are going to see an upsurge of shrinking
insulating epoxies which will pull the BGA into electrical contact and
underfill
it, at the same time: a very cheap and reliable method of interconnection
with
long-term reliability thrown in, provided the substrate and the component
are
perfectly clean at the outset.
Brian
Paul Klasek wrote:
> Agree, Anil definitely speaks from experience, having here one fellow ex
> TATA in Bombay,
> the horror stories (perfect antistatic environment as the condensations
runs
> from tables) are real .
>
> Disagree, Brian , getting puzzled how the hell shall i achieve this high
> reliability with this "unwashed" SBGA (2x2 inches square just about)
sitting
> some .5mm above the board, on my desk .
> Hmm, lucky me on no clean, don't envy you the washing machines .
> >From my limited view i'd say the times of cleaning shall change this
> millenium
>
> cu paul
>
> -----Original Message-----
> From: Brian Ellis [mailto:[log in to unmask]]
> Sent: Saturday, 1 January 2000 18:19
> To: [log in to unmask]
> Subject: Re: [TN] Harsh Environments?
>
> Anil
>
> Yes! I agree that this does not help. However, a French client of mine has
> traced
> wind-borne sea salt inland under some weather conditions, so this factor
may
> be more
> serious than is commonly thought.
>
> The strategic computer room of a UK Royal Navy ship, placed right in the
> interior of
> the structure, is equipped with the most sophisticated air
> conditioning/filtering. One
> such ship, in dock for refitting, had a fitter wedge the door open for a
job
> he was
> doing where space was limited, for a couple of days during what was
reported
> as winds
> of 3 -4 Beaufort. I was informed that malfunctioning of some equipment
> occurred and,
> as a safety measure, the totality of the equipment was replaced. This was
> reported to
> me by an ex-Ministry of Defence employee.
>
> Even worse is salt scattered on roads for ice prevention. The wheels of
> passing
> vehicles throw up a mist of concentrated brine which spreads everywhere.
>
> I reported these phenomena in my book published in 1986.
>
> Brian
>
> Anil Kher wrote:
>
> > Upto 1 km inland of coastal areas and during monsoon there is 50 ppm of
> salt
> > in the aerosol owing to heavy surf / winds. This tends to enter the
> > electronic instrument chasis and can condense at dew point on the PWB.
> > This environment would be HARSH.
> > Anil Kher
> > ----- Original Message -----
> > From: Brian Ellis <[log in to unmask]>
> > To: <[log in to unmask]>
> > Sent: Wednesday, December 29, 1999 12:47 PM
> > Subject: Re: [TN] Harsh Environments?
> >
> > > David
> > >
> > > Sorry, I'm not with you on this one. 20 - 25°C/40-80% RH is a
perfectly
> > normal
> > > office-type environment. In my view, a mildly harsh environment starts
> at
> > about 35°C
> > > XOR a RH > 80% or a harsh one at 30°C AND > 75% RH. Where I live, we
> have
> > summer temps
> > > up to 47°C with low RH and our car electronics (even radio and
> > window-winders) perform
> > > normally after the car has been sitting in the sun and you cannot
touch
> > anything
> > > inside, it is so hot. Last night, in midwinter, the temp dropped to
13°C
> > and there was
> > > an equivalent dew point, indicating 100% RH, with c. 1 mm of
> precipitation
> > in the form
> > > of condensing dew. Again, external electronics worked fine, including
> > cheap movement
> > > detectors. I cannot be persuaded that either of these conditions are
> > really "harsh", so
> > > much as normal.
> > >
> > > The ionic contamination is not part of the environment and a cut and
> dried
> > figire of
> > > 1,5 µg/cm2 eq. NaCl is meaningless without knowing the applications,
> type
> > of circuitry
> > > etc. In some cases, with low voltage gradients, this level would be
> > perfectly safe even
> > > at 80°C/90% RH. On some HDIS circuits with high voltage gradients,
even
> > 1/10 this level
> > > may be dangerous, provoking something akin to Doug Paul's arc welder.
> > >
> > > I honestly do not believe one can be categorical about this kind of
> thing.
> > Perhaps you
> > > would like to expound further as to your reasoning????
> > >
> > > Have a good pre-millennial year
> > >
> > > Brian
> > >
> > > David Douthit wrote:
> > >
> > > > Technetters,
> > > >
> > > > I would like some expert opinions on what constitutes a "harsh
> > > > environment".
> > > > In order to stimulate some debate the following is one proposed
> > > > definition.
> > > >
> > > > "Due to the highly competitive nature of the electronics industry
and
> > > > costs of coating the issue of whether coating is required or not can
> > > > become a hotly debated topic. The primary issue is "What is a harsh
> > > > environment?".
> > > >
> > > > The following general rules can be considered as the boundary line
> > > > condition for a "harsh environment". There are three minimum
> conditions
> > > > which must exist in the localized area of the circuitry at the same
> time
> > > > with or without power applied:
> > > > 1. A relative humidity of 60% or higher.
> > > > 2. Temperatures above 0 degrees C.
> > > > 3. The deposition of ionic contaminates on the circuitry surface
which
> > > > will exceed 1.5ug
> > > > of NaCl or its' equivalent per square cm during the expected
> > > > lifetime of the product.
> > > >
> > > > Consideration of these conditions must also include shipping,
storage,
> > > > and handling of the product. These conditions are a reference point
> and
> > > > exceptions are possible. Researching these environments are required
> to
> > > > determine if these conditions exist."
> > > >
> > > > Thank you for your time.
> > > >
> > > > D. A. Douthit
> > > >
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