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Subject:
From:
Russ Winslow <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 1 Apr 2000 19:46:14 -0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (180 lines)
Ken,
First you should rule out the possibility of board failures.  Assuming you
have done this:

I have seen this happen twice in my career.  In both cases the components
were alloy 42.  In both cases  cerdips went into a preclean bath that was
contaminated with copper.  The copper plated out onto the alloy 42 instead
of the alloy 42 being cleaned.  This gave the components a nice solderable
copper finish.  But underneath was a disaster waiting to happen.  No one
noticed the copper plated cerdips.  I bet they looked pretty funny before
solder dip.  These units then found their way into some commercial jet
engine control boards.  After about 100 hours of engine testing they started
failing.  These were thru-hole cerdips with nice fillets on both sides of
the boards yet they became electrical opens.  Fortunately they failed during
testing and not in the air.  Fortunately for me, my company didn't make the
mistake.

The Cypress TSOP's are assembled in the Philippines, Korea, or Taiwan.  It
appears that Hyundai (Chippac), Amkor (Anam), OSE, and Cypress Philippines
all use the copper leadframes with a Tin/Lead Plated finish (Sn85-Pb15) or
(Sn90-Pb10) for Cypress TSOP's.  All use silver spot plating for that 44
TSOP II package.  If you can pick up the part with a magnet then it's alloy
42 and your answer is probably easy.  My experience shows that a component
with this type of problem will not pass an 8 hour steam age/solderability
test.

You may want to have a cross section done then analyze the interface for
anything that doesn't belong. For copper with a solder finish you should
find only copper, tin, and lead.  You might find a trace of silver left over
from the spot plating of the die attach pad.  Assuming you are correct that
the lead (leed) is soldered to the board but there is an open between the
board and the component then some seriously bad plating should be easy to
find when you cross section the solder joint.  Pulling the lead (leed) apart
with a needle as Phil recomends should work fine too.  Save the pieces for
analysis.

Hope this helps

Russ Winslow
Six Sigma
1940 Concourse Drive
San Jose, CA  95131

(408) 526-1350 x 1


-----Original Message-----
From: Phil Crepeau [mailto:[log in to unmask]]
Sent: Thursday, March 30, 2000 10:26 AM
To: [log in to unmask]
Subject: Re: [TN] Solderability of TSOP...


hi,

you are certainly correct about this, and i'm glad to have an opportunity to
clarify the intention of my response.  this technique was offered as a tool
to get to the bottom of a very strange situation where intermittents were
being experienced yet there was no visual indication that the component
lead-to-board connection was defective.  it has worked for me.

you definitely wouldn't want to do this as a normal inspection process.

phil

-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Thursday, March 30, 2000 10:13 AM
To: [log in to unmask]
Subject: Re: [TN] Solderability of TSOP...


Haven't we had this discussion before?  My fear would be that following
Phil's advice will CREATE fractured solder joints.

Bev Christian
XLTEK

-----Original Message-----
From: Phil Crepeau [mailto:[log in to unmask]]
Sent: March 28, 2000 7:25 PM
To: [log in to unmask]
Subject: Re: [TN] Solderability of TSOP...


hi,

you should try to gently move each lead, side-to-side, with a fine needle.
this should find any fractured solder joint that your microscope may
overlook.

phil

-----Original Message-----
From: Ken Patel [mailto:[log in to unmask]]
Sent: Tuesday, March 28, 2000 3:25 PM
To: [log in to unmask]
Subject: Re: [TN] Solderability of TSOP...


Bev,
You are right in catching and educating me on Alloy 42, lead material v/s
plating. As the data sheet doesn't show the lead material & plating for 44
pin TSOP, I have assumed that the plating will be same as 32 pin TSOP which
is copper leads.

We do not see any failure visually using regular microscope, it's a big
problem for us on this thin TSOP. If any of our technetters has found
similar situation and how it was resolved will help us in getting at the
bottom of the problem. I have asked Cypress for lead related info with type
of plating and will ask our test guy if they can nail it down to particular
pin for further microscopic inspection.

re,
ken patel

At 02:19 PM 3/28/2000 -0500, Bev Christian wrote:
>Ken,
>First I don't think you really mean to say the part leads are made with
>eutectic solder or Alloy 42.  The leads are either Alloy 42 or copper, with
>a lead finish of eutectic solder, other tin/lead solder alloy or maybe even
>TI palladium.
>
>So you have sufficient pads size for good fillets, good soldering of other
>parts, good profile and heel fillets.  Hmmm.  My question would then be, do
>the failures look like the lead has pulled right out of the fillet, with
>bare lead frame material showing.  If this is the case and the leads are
>indeed Alloy 42, then this has been seen before, is related to the final
>processing of the Alloy 42 and I think has been discussed here on TechNet.
>Check the archives.
>
>regards,
>Bev Christian
>XLTEK
>
>-----Original Message-----
>From: Ken Patel [mailto:[log in to unmask]]
>Sent: March 28, 2000 1:27 PM
>To: [log in to unmask]
>Subject: [TN] Solderability of TSOP...
>
>
>Guys,
>We have encountered problem related to component solderability, looks like!
>We are using Cypress Semi TSOP (SRAM-SM 71016 64kx16, ASYNC TSOP-44). This
>part has very small foot area which make a direct contact with the pad on
>the boards.
>
>The problem we have encountered is that many boards fail at ICT but will
>pass once we touch it up using solder iron. Solder at the TSOP location
>looks good and also in the surrounding vicinity. I do not see any profile
>problem. There is no toe fillet but I can see the heel filet rising on the
>lead. Pads are designed longer so that parts made by others can fit too.
>
>What can be possible causes of the problem? I tried look at the WEB but
>looks like parts are made using eutectic solder and not Alloy 42 but can't
>ruled out it was not specifically mentioned.
>
>
>re,
>ken patel
>______________________________________________________
>Ken Patel                       Phone:  (408) 490-6804
>1708 McCarthy Blvd.             Fax:    (408) 490-6859
>Milpitas, CA 95035              Beeper: (888) 769-1808

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