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July 2005

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Subject:
From:
Jack Crawford <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Jack Crawford <[log in to unmask]>
Date:
Mon, 25 Jul 2005 11:20:58 -0500
Content-Type:
text/plain
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text/plain (116 lines)
Richard, your question seems to be posted for IPC specifically but was
placed on TechNet.

J-STD-020C Clause 4 has a note under Tables 4-1 (SnPb Process) and 4-2
(Pb-free Process) that states:
Note 4: Components intended for use in a ''lead-free'' assembly process
shall be evaluated using the ''lead free'' classification temperatures
and profiles
defined in Tables 4-1, 4.2 and 5-2 whether or not lead free.

Component classification should be established by the manufacturer
towards the most demanding assembly process. Companies reclassify
components when those components are manufactured with characteristics
that enable use in LF mfg. 

I'll share your recommendation to have multiple classification levels
with the committee. However, industry is having a hard time correlating
part numbers to lead finishes and I'm not sure there will be buy-in for
multiple process temperature classes as well. 

Jack


Jack Crawford, IOM
IPC Director Certification and Assembly Technology 
[log in to unmask] 
847-597-2893 
FAX  847-615-5693 
3000 Lakeside Drive, Suite 309 S
Bannockburn, IL, 60015

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard
Sent: Monday, July 25, 2005 8:29 AM
To: [log in to unmask]
Subject: [TN]

Jack,
I have had experiences lately with components that were formerly a class
3 MSD level coming in now classified as a class 5 or 5A, because the
termination finish was changed to a lead-free finish. Apparently the
component vendors feel that if they provide a lead-free finish, they are
implying the component can undergo a lead-free process with a higher
reflow temperature. To ensure the components survive the higher reflow
temperatures seen in the lead-free process, they call out a higher MSD
level, typically upgrading by a factor of two. This means that we will
receive the same part with different MSD levels. This causes us to
handle components as if they are a level 5A when they are actually a
level 3, even though we are using only the leaded process and reflowing
at the lower solder temperatures.
As seen by the rash of emails back and forth in the Technet Forum,
apparently I am not the only one with this problem. Many of us are not
required to change over to the lead-free solders (heavy industrial
equipment, military suppliers, etc.).
The "fix" for this problem seems to be very simple. I am wondering if
the J-STD-020 cannot be changed to call out two different MSD levels,
one for use on tin/lead processes, and one for use on lead-free
processes.

We know that the change in the part number to signify a lead-free finish
controls whether the part is lead-free. However, the package does not
change. So we should be unaffected if our purchase order calls out the
non-leadfree component part number, right? Well, the problem is that
most component vendors discontinue the lead-bearing finish as soon as
the lead-free finish is available. This leaves us no choice except to
purchase the lead-free part and handle it at the higher MSD level. But
the part itself has not changed. So why should we have to handle it
differently if neither the part nor our process have not changed?

Most disturbing, why did the part vendors not discuss this with IPC? We
have seen no communications from anyone on how this was being handled.
It would have been much easier to come up with a two-number rating
system that indicated the handling requirements based on the intended
process.
If not, then some type of historical preservation system should be put
in place for those who will not change to a lead-free process, so that
we do not place unnecessary limitations on floor life and bake out times
without reason to do so.

To further complicate the problem, many component vendors did not even
change their part numbers when they changed over to a lead-free finish.
I actually have several parts that come in both tin/lead and tin-only
with the same exact part number. I have no way of knowing which lots are
which. The part number never changed.

Some type of controls have to be placed over this situation.
Historically the industry depended on the IPC to provide this. The
problem is not a minor one, it has severe impact on material handling
cost for thousands of different OEMs and CEMs worldwide.

This is a major problem. Can you tell us what the IPC is doing to
address this?

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