- Components are generally robust and compliant with lead-free processing, thus allaying some earlier concerns over component stability.
- Some components do exhibit significant damage because of the lead-free processing and give cause for concern, i.e. both polyester and electrolytic capacitors. This poor performance is attributed in part to their wound and laminated construction. Although the capacitance will remain within quoted tolerance levels, the loss tangent for these capacitors can degrade to values well outside the tolerance levels.
- Care should be taken not to darken LED-casing materials due to overheating, which would reduce light emission levels.
- Examples of problems with misalignment of ultra-fine pitch QFP after lead-free soldering which do not occur with conventional SnPb.
- Studies have shown that temperature differentials across boards can be as much as 50K. For large boards with a mixture of large and small components, or for those using smaller reflow ovens, overheating of components may be more likely, and correct temperature profiling will be critical.
- The increased temperatures associated with lead-free soldering have little or no effect on dimensional stability or surface insulation resistance of laminate.
- The higher glass-transition temperature (Tg) laminates exhibit better resistance to bend at higher temperatures.
- Low Tg laminates used in lead-free technology may become warped. Such might arise from a variety of circumstances including uneven multilayer build, reflow of a heavily populated assembly when supported only in the four corners of the substrate, or reflow of a heavily populated assembly using an edge conveyor without additional central supports.
- Components and PCBs that are susceptible to moisture ingression and subsequent delamination are likely to have increased susceptibility, due to the higher reflow temperatures and possible faster heating rates. Care should be taken to protect components and PCBs by ensuring that they are delivered in suitable packing (shrink-wrap is generally insufficient), and that they should remain in this protective packing until immediately before the assembly.
- The solderability of the PCB pads is largely independent of laminate material, but will be dramatically influenced by subsequent heating cycles. The increased ageing associated with the higher lead-free temperatures (compared with SnPb profiling) will cause a significant reduction in solderability of all laminates types. If standard immersion gold finishes are used for lead-free assembly (where multiple profiling will occur, e.g. with double-sided soldering), then lower yields can be expected on the second-side reflow compared with those currently achieved with SnPb double-sided soldering.
