 Lead Free Introduction
Faced with regulatory pressures and increasing consumer awareness of environmental issues, Melexis is required to deliver lead free package alternatives for their products. Lead (Pb) content in the packages is limited to the terminal plating, and it is already very low indeed. For a JEDEC SO20 package for instance, the lead content in the package is only about 1 mg or 0.2%. Depending on the total weight of the customer’s product, this may be low enough to be accepted as lead free (e.g. <1000 ppm).
More important is the soldering material used in the board assembly of the components. Lead free components will only really make sense if subsequently board-assembled will use Pb-free solders. Since such solders typically melt about 30°C higher than the eutectic tin-lead (SnPb) composition, the lead free soldering process degrades or may degrade the package in JEDEC moisture sensitivity level, and potentially has an adverse impact on short term (failures after soldering) and long term (failures after temperature stress in the field) reliability.
Material choice
For packages with terminals (the term « leaded » packages will be obviated here, to avoid confusion), the prime choice of Melexis for plating is pure matte tin. The traditional concern is whisker growth during storage. Tin whiskers are recognized as a reliability concern throughout the industry. To mitigate whisker growth Melexis has implemented a post-plate annealing of 1 hour at 150°C within 24 hours of plating.
Forward/Backward Compatibility
- Backward compatibility: A lead-free component is said to be backward compatible if it can be reliably attached to a PCB using tin/lead solder paste with a tin/lead solder profile (typical peak reflow temperatures ranging from 220°C to 235°C).
- Forward Compatibility: A SnPb component is said to be forward compatible if it can be reliably attached to a PCB using lead-free solder paste with a lead-free profile (typical peak reflow temperatures ranging from 240°C to 260°C).
- For leadframe-based surface mount packages
Lead finish |
Reflow Process and Peak Temperature Range |
Tin/Lead Process
(220°C - 235°C) |
Lead-Free Process
(240°C - 260°C) |
Tin/Lead (SnPb) |
OK |
OK if device qualified for
260°C (forward compatible) |
Lead-free (matte Sn) |
OK (backward compatible) |
OK |
|
