Unfortunately, I cannot run from the boards, because our customer asks ME
what to do.
They say that they have used such boards for years without problems and I'm
temptaded to say to them 'OK go on then', but at the same time, I will loose
my face if the equipments for these boards will crash in Poppystan. I will
write something to them after considering even answers from TN gurus.
Inge
----- Original Message -----
From: "Joyce Koo" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 07, 2009 4:40 PM
Subject: Re: [TN] Need clever comments
whisker grow to release mech stress, caf is electrochemical?
Look like you have poor board house on hand. Are you sure they are mil
house? Or mil site house? Many change location and all the qualitu go
without.
Stress in the copper appear to be high, the cupper extrusion might initially
covered by thin layer of solder mask. Rough surface of conductor may
contribute thin localized solder mask, extreme case, nodula surface not
covered.
Press fit? You must be using tin male connector on the other side.
Normally, you do need Ni, crack under plating layer? Ni-P? If it is
electroplated Ni, your vendor can not plating the non crack under lining?
Inge, run like hell away from them. Pay someone handsome money and re make
the board.
--------------------------
Sent using BlackBerry
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Mon Sep 07 07:21:54 2009
Subject: [TN] Need clever comments
Hi all, need some professional backup regarding MIL quality boards.
Objects: FR-4 Class III double-sided multi-layer boards, populated with
SOICS, BGAs,and a lot of passive components.
Observation 1 : the non soldered board have lots of Tin whiskers on inside
of the PTH barrel. My thought is this: if whiskers can grow long before the
board is assembled, then ain't it likely that even CAF can be generated?
See photo 1.
Observation 2: Copper has somehow penetrated the solder mask. This can be
found everywhere along the conductor traces. You need a very good light
microscope and a SEM to see it. See photo 2.
Board data: Copper with 0.8 micrometer Immersion Tin. No nickel barrier.
Solder mask thickness not specified.
Application: Typical MIL-883 environment
Q1: What is your opinion about that thin Tin directly on copper? I dislike
the concept. Copper is very mobile at high temperatures, and combined with
humidity, there can be leakage currents and corrosion issues. Even if the
boards are CCd, there is a risk with copper .
Q2: I gave the advice to introduce a nickel barrier, but our customer
claimed, that they can't because of pressfit connectors and pressfit test
pins on the board. Furthermore, they had heard that one cannot have nickel
platings when pressfitting, because the nickel will crack and oxidize and
cause electrical disfunction. Is this your opinion too? Are there any
relevant testing behind such statements?
Thanks in advance
Inge
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