Steve, couldI have your telephone # so that I could talk to you about our
TSOP experiences?

-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: Friday, February 18, 2000 4:38 PM
To: [log in to unmask]
Subject: Re: [TN] Alloy 42 Leaded TSOPS


In a message dated 02/18/2000 1:14:55 PM Central Standard Time, 
[log in to unmask] writes:

<< We have a sole source for TSOP components, in which, they are only
 available with alloy 42 leads. The vendor refuses to build the parts with
 Copper leads because the  CTE of alloy 42 better matches the die CTE and as
 result they have fewer component failures and defects.
 
 Does any one know of a PWB material that would better match the CTE of
alloy
 42 leaded TSOPs? >>

Ahh that's the rub ain't it? The component vendors dictate what materials 
they use to improve their numbers, it's up to us assemblers figure out how
to 
deal with it...just like Texas Instruments palladium plating. I understand 
that when they switched from tin/lead plating to palladium their yeild 
increased dramatically...

Well seeing how alloy-42 CTE is down around 5.5ppm /° C., there's a few 
exotic laminates that come a little closer than FR4 to matching that CTE,
but 
I said just closer. I got this outta my Printed Circuits Handbook:

Laminate Type(Fabric/Resin)     CTE in X/Y axis

Aramid/Epoxy                        6.5 - 7.5ppm /° C.
Thermount/Polyimide             6 - 10ppm /° C.
Thermount/Epoxy                 7 - 9ppm /° C.
S-2 Glass/Cyanate Ester         7 - 10ppm /° C.
Quartz/Epoxy or Polyimide           8 - 11ppm /° C.

Also in the book there is this statement; "While adequate solder joint 
reliability can be achieved with TSOP's in many situations, some vendors
have 
opted to encapsulate the solder joints with a filled epoxy to better 
distribute the stresses."

I have never gone to that extreme, and have used TSOP's in quite a few 
assemblies.
Worked at a memory company where we built literally thousands of PCMCIA
Flash 
cards using TSOP's.

There is also the option of turning the TSOP into a MicroBGA if it's Flash 
Memory. A lot of memory component vendors are going that route, and 
supposedly a MicroBGA is more reliable than a TSOP...smaller too.

-Steve Gregory-

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