Out-of-tolerance zero ohm resistors - Page 4

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Re: Out-of-tolerance zero ohm resistors
On 6/1/2015 3:28 PM, John Larkin wrote:
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You are such a trip... lol

--  

Rick

Re: Out-of-tolerance zero ohm resistors

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Well, a BGA ball doesn't sit very stably on a solder-coated
convex-bump pad. Try stacking two basketballs; the upper one tends to
slide off.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: Out-of-tolerance zero ohm resistors
On Mon, 01 Jun 2015 17:08:20 -0700, John Larkin

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  Not if you put these on 'em...


https://www.youtube.com/watch?v=bI06lujiD7E


Re: Out-of-tolerance zero ohm resistors

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  You lack co-planarity.

Re: Out-of-tolerance zero ohm resistors

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[...]

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I know I posted this before but...

http://ee.devereux.me.uk/IMG_0216.jpg


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John Devereux

Re: Out-of-tolerance zero ohm resistors
Gave us:

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  Piss poor stencil thickness leading to piss poor job..  Piss poor
paste efficacy.  Likely left out too long before reflow as well.

  It had/has not a goddamned thing to do with the gold PCB pads.

Re: Out-of-tolerance zero ohm resistors

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Nope, you couldn't even solder to a bare board with a soldering iron. I
think there must have been some kind of contamination on the surface, a
very thin residual layer of solder resist possibly.

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It's just funny. The parts fell off when I tapped the side of the board.

Re gold; it is easier for assemblers to work with and probably better
quality overall but I do not believe it is the most common finish
overall, due to the added cost. Sure you will see it for lower quantity
production and a lot of high-end stuff.

--  

John Devereux

Re: Out-of-tolerance zero ohm resistors
Gave us:

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  Which obviously means that no paste was screened onto the board to
begin with.  DOH!

  Even the parts that had paste and minuscule fillets would not pass as
sufficient.  Yer process controls and QA inspectors are fuxed up.

  The paste needs to be kneaded for a half hour before it even leaves
the jar, minimum.  Then, it has to be fresh.  Then, the stencil has to
be thick enough ton actually apply it to the PCB, and the windows need
to be large enough to actually get enough on the pads to perform a basic
soldering operation.  Then, it needs to go into the reflow oven without
sitting somewhere for hours on end first.

  You may also want to attach certain parts with SMD adhesive as it
appears the placer programmer cannot even sit a chip down where it
belongs...  You know...  PROPERLY registered.  I saw quite a few
problems and would blame none on the gold plating.

  That is, of course, considering that is what ended up on the board.  I
would question the PCB fab house as well.  Especially since you claim
that you could not even "wet" the board with a hot, hand held iron.

  I would also question your choice of flux, and even consider a
de-oxidation session on the boards before they get pasted.

Re: Out-of-tolerance zero ohm resistors

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Of course it was. You could see the balled up solder on the parts.. Plus
everyone else is not as stupid as you assume.

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Nope.


maybe but it was nothing to do with that.


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yes quite, that is the givaway that it is nothing at all to do with
anything other than the bare boards as received. It was the same for
unprocessed boards by the way.

The bare board supplier admitted a problem on their side, the person
responsible was "looking for other opportunities", to use their charming
euphemism.

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--  

John Devereux

Re: Out-of-tolerance zero ohm resistors
Gave us:

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  There is a definite time limit between pulling the paste and reflowing
an assembly.  Breach that RULE, and you are asking for failure modes,
then you stand around looking for others to blame.  Nice try.

Re: Out-of-tolerance zero ohm resistors

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Yes I know, they know, they didn't.

It amazes me, the absolute certainty with which you are able to
pontificate from the other side of the world, about something that
happened 15 years ago, where you know nothing of the particulars or the
people involved. Even when you are told the actual, easily proven
reason, no, it was something else, entirely from your imagination.


--  

John Devereux

Re: Out-of-tolerance zero ohm resistors
Gave us:

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  15 years ago?  Even easier to pontificate about their lack of
knowledge or expertise in the field.

Re: Out-of-tolerance zero ohm resistors
On Tuesday, June 2, 2015 at 10:34:56 AM UTC-4, John Devereux wrote:
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Do whatever steps you want, if
You have cleared them with the Pontiff... (Tom Lehrer)

Cheers,
James Arthur

Re: Out-of-tolerance zero ohm resistors
Gave us:

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  Their fine print says "It *looks* like gold, but it is really brass,
and a bad alloy of that even.  :-)

  Gotta read that fine print.  BAD fab house!

  I'd sue, big time.

Re: Out-of-tolerance zero ohm resistors
On Tue, 02 Jun 2015 15:00:31 +0100, John Devereux

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Was this the so-called "black pad" issue?  

(caused by corrosion of the Ni barrier layer during the Au plating)  

I've not (knock on wood) seen that yet.  

--  
Best regards,  
Spehro Pefhany
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Re: Out-of-tolerance zero ohm resistors

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It could have been, although I would have expected the pads to look
black then instead of gold? (After reflow).

My theory was it might be incomplete processing of the solder resist
removal stage. So there was an invisible layer of very thin resist. But
it was just a guess, I did not get the exact details (just replacements).

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--  

John Devereux

Re: Out-of-tolerance zero ohm resistors
On Tue, 02 Jun 2015 18:27:04 +0100, John Devereux

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Seems like they are black where they separate after the part falls
off.  

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Was it LPI mask? That would make sense.  

--  
Best regards,  
Spehro Pefhany
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Re: Out-of-tolerance zero ohm resistors

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On my board the pads were covered with paste before reflow, so the
solder should have wetted the gold (I would think). But it didn't.

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Yes LPI solder resist.

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John Devereux

Re: Out-of-tolerance zero ohm resistors
On Tue, 02 Jun 2015 13:28:39 +0100, John Devereux

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Did the parts separate from the solder, or did the solder separate
from the board?


--  

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

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Re: Out-of-tolerance zero ohm resistors

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The solder would not wet the board. The solder was there it was just
repelled from the pads and ended up entirely on the "pins". it was due
to a thin layer of solder resist or some such over everything (as
detailed in another post).

You could try to tin the pads manually with an iron, nothing unless you
scratched away the invisible layer.


--  

John Devereux

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