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

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************