It's beginning to be visible Gaby :
2 stack ceramic , one (bottom I presume) dipped, one gold on top .
1206 or 0805 presuming again ; with quite likely 3-4%Ag alloy:96, (common
high temp),
soldering the stack together .
Than you take this sub, assemble with rest of componentry in 63/37 ;
and pass this stack through say 230'C without additional solder .
Than you find the crack , (WHICH WAS NOT THERE BEFORE [?]).
Well ; from my simple logic the crystalline formations on subsequent reflow
do move and retighten upon cooling differently,
and since the ceramo is not going to give a nanoinch it does crack ;
the Ag (suspected) IMT's may be hard at work on second pass (as I noticed
drastic accelerations on AuSn IMT's upon subsequent passes) .
Soo, my semieducated guess would be : hunt original (high temp alloy)
solder, Gaby,
if it's anything with 3%+ Ag ; when you mix it with a dose of Au on top,
and "soak" some life out of it too, in the end it's as brittle as sandstone
(metaphorically).
As far as I see it , there's your "BINGO"
With A bit of luck Werner, Guenter, or the rest of reliability academia will
reflect on this with some more specific memorabilia.
Anyhow ; march to TELETEC ; verify the alloy , and give them a free lesson
then (if it all clicks).
cu
Paul Klasek
ResMed
-----Original Message-----
From: Gabriela Bogdan [mailto:[log in to unmask]]
Sent: Sunday, 10 January 1999 16:37
To: Paul Klasek
Subject: Re: Soldering Solutions
It is a long story.Forgive me for taking your time, but if you want to
read it, here it is.
We produce a board for microwave applications by reflow soldering a series
of
custom made components among others.One of them is a drop in isolator made
by
TELETEC. I am in charge of performing the tests for reliability concerning
resistance to soldering heat, aso. This component is made against almost any
rules I know, but due to cost reductions we have to swallow the pill. One of
its features is a porcelain capacitor with gold finished terminations, piggy
mounted on another porcelain capacitor with solder terminations- I think,
because after soldering it is hard to tell. There are 3 such Eiffel towers
on a
little piece of FR4.
The coil and the resistor do not play a role in this scenario.
Now, what do I do first? - I pass the poor thing through the reflow oven on
a
bare board, just to see what happens. I let it cool down, beg forgiveness,
and
I put it under the microscope invading its privacy. At first it looks OK, no
component is displaced. Then I look closer at the solder connections between
the piggy backs, and BINGO! there is a fine gap with frayed borders between
the
two capacitors!
I put myself in the place of the manufacturer. He had to use a high
temperature
solder , otherwise the whole tower would go kaput. I go to my XRF to get
some
information, and it gives me a composition with high tin content. Of course
it
is not accurate under such conditions, but I do this often for comparison
with
63/37.
But, did he think about the compatibility with the gold terminations? And if
yes, did he do any tests? Maybe I did something wrong? Maybe the specific
capacitor is irreplaceable? Maybe only hand soldering is a solution? All
four
pads are under the base of the component- it can not be so.
I wrote all this to the manufacturer. Now you know.
Thanks,
Gaby
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################
|
