What works the best is to use commonly accepted Best Manufacturing
Processes. In this case, on the process detail sheets you call out the
specific solder, flux, solder tools, tips, and temperatures to be used
for that particular process on that particular product.
Not a general Standard Operating Procedure that is particular to a
process only, but on the particular detail for the specific product to
be soldered.
You don't do that, you depend on the operator's expertise, you say?

Sorry, your process is then out of control.

General 5S procedures should be used to keep solder, solder tools, tips,
fluxes, etc. in visible control on the benches, including signage to
control the benches themselves. Color coding no-clean, water-soluble,
and lead-free fluxes and solders for visible management is the first
step. Training and certification of the assembler so he/she knows what
each is used for (and not used for) is another step. Once the operator
is trained and certified, you shouldn't have to worry about improper use
of the wrong tools or materials. It is always the manufacturing
engineer's responsibility to keep the process in control, and proper
documentation of tools, methods, and materials used is part of that.
Keeping lead-free tips and soldering systems in a separate bench to
avoid cross-contamination of alloys left on the tips is a commonly used
practice, and a good approach. Segregation without training does not
work, as it is too easy for an uneducated operator to "borrow" the wrong
materials for the product. Training without segregation can be done, but
it is much more difficult to prevent the wrong tips and tools from being
used. The workbench or station that the process should be done at should
also be called out on the process detail, just like any other tool or
material.
It is not always economically feasible to segregate an entire SMT line
for Pb-free products. In that scenario only the printer needs tight
controls over the solder paste to be used. The workstations for solder
rework (touchup rework) and post-SMT assembly and soldering should be
segregated into Pb-free and non-Pb-free. Although economically
prohibitive for some, the wave solder machine should never be used for
both processes.
Another area where segregation is not always possible is the Hot Gas
Rework area. The operator(s) in that area need to be very knowledgable
of the product they are working with in order to prevent the wrong
materials from being used. While specific detail for reworking every
possible component on a given product is not possible, a rework detail
sheet can be provided in the product-specific instructions that calls
out the appropriate process materials and methods to be used for
reworking that particular product. Examples such as notations not to
wash a no-clean board in the water-wash process, use only no-clean or
lead-free solders when performing rework, etc., etc., can be documented
as a reference for the rework operator. Some segregation is necessary,
but proper documentation, training, and certification is more important.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of bob wettermann
Sent: Wednesday, August 10, 2005 6:37 AM
To: [log in to unmask]
Subject: [TN] Hand Soldering-Mixing Sn63 and L-F Processes

Ladies and Gents:

There have been several ways discussed in the trade press and in papers
re: how to separate/keep separate Sn63 and l-f hand soldering tools and
materials. Some claim completely separate hand soldering tools are
required while others claim that separate tips are sufficient in
segregating the processes. Other larger companies have completely
dedicated mfg lines dedicated to l-f mfg and hence the hand soldering
tools are separated with respect to floor space. Does anyone have these
or other practical experiences on what works the best?

Bob Wettermann




Bob Wettermann

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