Steve Ross posted a TechNet inquiry about whether it makes sense to
impose a solderability requirement in parts procurement. The problems
with doing so are reduced availability, increased cost, and having to
use a different part number. He observes that he gets many good parts
without a solderability requirement, and sometimes parts purchased to
a mil spec do not have good solderability. Also, he says "No strong
evidence exists that suggests a field performance / reliability
concern." Hence he states that he can't see how to justify "raising
the bar", in spite of encouragement of "many experts" to do so, and
asks for practical philosophy. Here are my thoughts.
The easiest part of the answer is to state that the reason for requir-
ing solderability is for the factory to be able to get acceptable
connections without rework. The only way that poor solderability will
reduce product reliability is if someone, in order to get an accept-
able connection, uses heroic means and either causes concealed heat
damage or makes the solder look as if it had wet when it has not (what
might be termed "sculpture" or "camouflage").
The way to prevent heroic measures is with adequate training,
incentives, and supervision of the operator, inspector, and foreman
(foreperson?). That may mean not penalizing factory personnel for
failure to meet a delivery schedule if the cause (including poor
solderability) is out of their control. Incentivization may also mean
holding someone else in the organization (purchasing, receiving
inspection) responsible for allowing unusable material to reach the
factory floor.
Adequate solderability (including shelf life) is an implied
requirement of the part procurement, and a supplier's failure to
deliver it indicates a deficiency in their termination finish
operation, since means to achieve it consistently are well known. I
wish that I had more experience here in dealing with suppliers, but it
seems to me that someone who delivers parts that cause trouble should
be willing to respond appropriately, regardless of what's in the fine
print.
The parts most likely today to have solderability problems are the
commodity parts - the passives - allegedly because the tough competi-
tion and low profit margin make it difficult for the manufacturer to
pay for providing a robust finish. However, the very fact that these
parts are available from more than one supplier means that you have
the ability to buy from someone else, so it becomes more a matter of
whether your purchasing department is willing to give the order to the
supplier who has the best track record instead of to the lowest
bidder, and whether your factory is prepared to maintain and promptly
communicate the track record.
I hope this helps.
Gordon Davy
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