Mike,
In response to your comment about the gel coated automotive electronic
modules, I uploaded an old image of a non-descript corner of an engine
control module to the IPC site at
http://ipc-technet.groupsite.com/galleries/show/26944
We used to call the self-healing gel, "elephant snot", based on our
perception of what we thought the naturally occurring substance might be
like.
This material should be the poster child for Si materials having the
tendency to 'migrate'.
Steve Creswick
Sr Associate - Balanced Enterprise Solutions
http://www.linkedin.com/in/stevencreswick
616 834 1883
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Wednesday, March 05, 2014 2:38 PM
To: [log in to unmask]
Subject: Re: [TN] Aluminum fine-line PCB
Your field more than mine Joyce.
I just comment that the power die with multiple stitch bonds are used in
high rel circuitry (traction, cars, windmills, nuclear etc. The power
switching through these units (including through die tops) varies from
200-250 cranking amps in stop go auto systems, to many, many KVA in train
traction engines. Units are boxed but by no means hermetic, circuits are
protected by silicone gel, self repairing in case of transient arcing etc.
Regards
Mike
On 3/01/14 10:30 AM, Joyce Koo wrote:
> I believe it has attempted before (20 years or more ago). However the
> best
it can do is glass substrate metallization in terms of multilayer. Following
are the list of difficulty : aluminum is very Anodic.need to be well
protected. Pure al is weak,, and not that stable under high current (see
double wire bonds on some of the chips?). Oxidation of al is difficult to
control in an open environment. You got native oxide, but you have
hydroxide with various form, depending upon temp and pH. Under high field
you got voiding due to al can be easily diffused via influence of electrical
field. The die nowadays using Cu as part of solution for the inadequate
properties of al. Etc.etc. Gold, copper, appear to be less ęproblematic. AL
on glass with full sealed package, no problem. Again, my knowledge of al cct
is old story. Someone out there may invent something new today.
>
> "All professional skills are mastered by critiqued practice" - by Schon.
> Original Message
> From: Mike Fenner
> Sent: Saturday, March 1, 2014 7:10 AM
> To: [log in to unmask]
> Reply To: [log in to unmask]
> Subject: Re: [TN] Aluminum fine-line PCB
>
>
> Well you can solder Aluminium without flux. Three ways, some of which
> probably are capable of being used here, alone or in combination.
> 1) Scrubbing with Sn/Zn solder. Sn/Zn intermetallics are very hard and
will
> abrade the Al2O3 oxide, if done on point of melting you can achieve a
solder
> joint.
> 2) Ultrasonics can do the same thing with less skill involved
> 3) Use a reactive solder
> Possibly some combination of these could be made to work by
> - plugging the holes and reflowing
> - inserting wires and soldering them
> - using a sort of rivet and soldering heads Off the wall: People who
> make power modules have similar problems.
> In Google images search "DBC die wire bonds" and you will see quite
> thick wires and ribbons stitching die - some on multi levels. Also
> spring clip things bonded for vertical connections, might give you some
ideas.
>
> Regards
>
> Mike
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Jackson
> Sent: Friday, February 28, 2014 6:43 PM
> To: [log in to unmask]
> Subject: Re: [TN] Aluminum fine-line PCB
>
> Thanks Syed and Pat,
>
> Our challenge is making the connection between layers. We have used
> zincating to apply an Immersion White Tin finish to the boards and it
> works well, where there is aluminum. The trouble is with connectivity
> across the FR4/PI material sandwiched between the aluminum outer
> layers on vias and edge plating. Even though the dielectric is usually
> only 0.0021" thick (before pressing) the zincating doesn't adhere.
>
> We have a solder flux combo which does work well with the solder wick
> braid via solution we use today but we would dearly love to find a
> more elegant solution.
>
> - Paul
>
> On 2/28/14 8:58 AM, Ahmad, Syed wrote:
>> Electroless Ni after zincate over device Al pads is commonly used as
under
> bump metallurgy (UBM) for flip chips for solder ball attach/formation.
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Patrick Goodyear
>> Sent: Friday, February 28, 2014 10:50 AM
>> To: [log in to unmask]
>> Subject: Re: [TN] Aluminum fine-line PCB
>>
>> Paul,
>>
>> You can plate aluminum with zinc then nickel then copper. The zinc
>> keeps the aluminum from oxidizing the nickel replaces the zinc and the
>> copper over plates the nickel. I worked at a power plant, they use
>> various products to decrease the oxide layers on buss work not sure
>> what
> works on aluminum but they use Cool Amp (dry silver plate solution)
>> De-Ox-It a conductive grease and some other products. I think there
>> are some solders that will work with aluminum or low temp brazing
>> rod, I
> think it is all about the flux, Aluminum overlays an oxide layer
> almost immediately and that is a dang good insulator. TIG or MIG
> welding
aluminum
> is about the cover gas keeping the air out of the molten metal, my
> step
dad
> could weld aluminum with a Oxy acetylene torch, not a clue
>> how he did it. If you marry it with a dissimilar metal it will
>> cause major galvanic corrosion, I deal with it on a daily basis, using
>> stainless steel bolting in anodized aluminum mounting brackets. It
>> takes about 2 weeks and the stainless and aluminum become one large
>> white ceramic mess faster if the anodizing is disturbed. Look around
>> in the Utility industry since they use aluminum buss work all of the
time,
> and bolt it to copper.
>> Pat Goodyear
>>
>>
>> On Fri, Feb 28, 2014 at 7:39 AM, Paul Jackson wrote:
>>
>>> Hi Wayne,
>>>
>>> Thanks for the ideas. The sputtering is one we really hadn't
>>> considered and I am very interested into looking into it more.
>>>
>>> I'll send you the guide directly and if you are interested in seeing
>>> what the boards look like they are on the cover of Time magazine,
>>> Feb 17, 2014 edition.
>>>
>>> - Paul
>>>
>>> On 2/27/14 2:51 PM, Wayne Thayer wrote:
>>>> Hi Paul-
>>>>
>>>> A fascinating application!
>>>>
>>>> When plating copper into vias is not possible, or is inconvenient,
>>>> "macro-scale" designs use eyelets. You can't attach to inner
>>>> layers reliably with them, and I always found the external contacts
>>>> to be unreliable as well, so we made sure they were soldered on both
sides.
>>>> But they can look a lot more professional than braid, and lend
>>>> themselves to automation. I presume that your application would be
>>>> much tinier than any commercial eyelets and tooling sets could
>>>> handle, but theoretically you could probably come up with something
>>>> like that.
>>>>
>>>> Another possibility might be an organo-metallic paste like ORMET
>>>> sells, or perhaps some kind of sintering nano-metals. But either
>>>> of these options would probably have trouble getting through the
>>>> aluminum oxide to make a connection without some kind of assistance
>>>> from a suitable flux. Probably a lot of risky development would be
>>>> required for this path, but it has the potential to be scalable
>>>> down to your preferred geometry.
>>>>
>>>> Yet another possibility is that aluminum is commonly sputtered onto
>>>> silicon wafers, so why not get it deposited into the holes?
>>>> Activation and masking problems, but the prettiest and easily
>>>> scalable to tiny geometries.
>>>>
>>>> I don't understand your process (I'd like to get the little guide
>>>> available on your company's website, but for some reason it either
>>>> isn't sending out the email or my spam filter is eating it). But
>>>> another way people build interesting boards is to put the vias in
>>>> before the outer metal goes on.
>>>>
>>>> Wayne
>>>>
>>>> -----Original Message-----
>>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Jackson
>>>> Sent: Thursday, February 27, 2014 2:31 PM To:[log in to unmask]
>>>> Subject: [TN] Aluminum fine-line PCB
>>>>
>>>> Hi All,
>>>>
>>>> I'm new here to Technet so I'll ask you to be gentle, at least at
>>>> first.
>>>> We are manufacturing fine-line aluminum trace PCBs and our
>>>> customers are mainly wirebonding chips directly on the aluminum and
>>>> attaching components on selective copper pads. We are trying to
>>>> find a more elegant way to achieve through-hole connectivity than
>>>> our current method of filling vias with solder wick braid and
>>>> aluminum solder paste. It works but it's "fugly". The aluminum is
>>>> 30”m and the dielectric is typically 2.1mil. Any ideas would be
>>>> greatly appreciated.
>>>>
>>>> Paul Jackson
>>>> Omni Circuit Boards
>>>> (855) 798 9717
>>>> *w*ww.omnicircuitboards.com
>>>>
>>>>
>>>>
>>>> ___________________________________________________________________
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>>> --
>>> Omni Circuit Boards Ltd.
>>> 3-12760 Bathgate Way
>>> Richmond, B.C.
>>> Canada V6V 1Z4
>>>
>>> Tel. 604.276.9717
>>> www.omnicircuitboards.com
>>>
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