Frequently Asked Questions and Answers
Can the SMD components be processed in accordance with a 260°C soldering profile such as J-Std-020B?
Components with Pb-free finish may be reflowed with peak temperatures of 260°C (10 seconds). For resistors, no particular constraint is generally necessary on heating and cooling rates.
Can the through-hole components be wave soldered at temperatures of 260°C?
Pb-free through hole parts may be soldered with a 260°C wave without damage.
After the changeover, will the moisture sensitivity classification be altered?
This applies mainly to semiconductors with cavities that can take in moisture then rupture at the higher soldering temperatures. This does not apply to Welwyn resistors.
Will the changes to the component and/or the increased processing temperature affect value stability or reliability?
The standard resistance to solder heat test carried out for many years on our through hole and SMD parts is at 260°C, and the stability figures given on our datasheet relate to tests at this temperature. We do not consider it likely that routinely processing resistors at this higher temperature will adversely affect reliability.
Will the order number change after the changeover?
The order number will not change as the Pb-free parts are backward compatible with existing SnPb soldering processes, so most customers can accept either finish during a transitional period.
Is there any way to specify SnPb or Pb-free when ordering?
Customers requiring guaranteed Pb-free product before the end of the transition period must make this clear at time of ordering. WEEE / ROHS exempt customers requiring continued supply of SnPb finish should discuss this with Applications Engineering.
How will changed components be identified physically?
Pb-free parts will be identified by a Pb-free label ("Pb" in a circular prohibition symbol) on the packaging - label diameter approx 12mm.
What finish will be used on Pb-free terminations?
The termination finish on most parts is 100%Sn. For through-hole products this is applied by a hot tin dip process to avoid tin whisker growth. SMD chip parts are Sn plated on a Ni barrier, which also prevents tin whisker growth. For solder dipped parts (like W20 and WH series) the alloy used is SnCuAg - this is compatible both with conventional 60/40 SnPb solder and, at an appropriate temperature, with Pb-free solder.
If you have a specific request regarding Welwyn Resistors, please click the "Contact" tab above and provide details of your requirements in our response form.
Case Studies
Chip Resistor Replaces Surface Mount Wirewound
When a major manufacturer of industrial circuit breakers wanted to re-engineer their core range of products, one area of focus was on how to provide power resistive products in an SMD assembly...
