Material/Process Management
Below are some frequently asked questions that you will encounter in the transition to lead-free processes.
Are you ready for Lead-Free Assembly? (DOC 169kB)

Q: What About Solders?
A: Tin lead solder pastes melt at 183°c while lead-free pastes require 220°c. The temperature of the soldering iron may need to be increased, and the temperature rating of components will need to withstand these elevated levels. The alloys used in lead-free solder can vary depending on the application, but it is generally safe to use the 99C alloy (99.7% tin, 0.3% copper) for lead-free hand soldering, as this is compatible with most lead-free alloy options. Silver is added to some lead-free solder pastes to assist with the wetting and joint formation during the rapid reflow phase of typical surface mount technology assembly processes.

Q: What is the "Popcorn" Reaction?
A: Molded components can gather moisture when heat is rapidly applied. Above 100°c the moisture expands and becomes a gas. It tries to expand through the molded compound and, unable to escape it tends to break or pop the molding compound like a "popcorn effect". The industry has introduced a number of procedures for getting around this by baking and sealing the component.

Q: What if I need to maintain or repair my present equipment after July 2006?
A: The use of "banned" substances in spare parts to repair equipment put on the market before July 2006 will be permitted, but will not be allowed in new equipment.

Q: Will Prices Increase?
A: The European Commission estimates an average cost increase of between 1% and 2% for most WEEE products and 3% to 4% for a few large or more complex products. However, some suppliers have no plans to increase prices in the short term, and it is likely to vary from product area to product area.

Q: What is Whiskering?
A: Whiskering is a naturally occurring phenomenon that results in the spontaneous and unexplainable growth of tiny, needle-like protrusions, which break loose, short-circuiting system boards and terminals - seriously crippling or destroying entire systems.

Q: Issues relating to lead-free solder?
A: Soldered surfaces must be free of lead to begin with. This includes the PCB as well as the component. Lead contamination on a lead-free solder joint will significantly reduce the reliability of the joint.

Q: What about Temperature?
A: All lead-free alloys melt at a higher temperature than traditional tin-lead alloys. The temperature of the soldering iron may need to be increased, and both the components and PCB will need to withstand these higher levels. Increased temperatures also place a greater demand on the flux, and it may be necessary to opt for a higher solids content, or more active flux if the soldering becomes difficult when using lead-free materials. Typical melting points:
Tin-Copper 227°c
Tin-Silver 221°c
Tin-Silver-Copper 217°c
Tin-Silver-Bismuth 205°c to 215°c
Tin-Zinc 199°c
Tin-Lead 183°c
Tin-Bismuth 138°c

Inspection
Lead-free solder joints have a different appearance to those of tin-lead. They are usually quite dull, and the spread is less, resulting in fairly steep contact angles at the perimeter of the solder joint, where the solder meets the substrate. This does not mean that the joint is faulty. Studies suggest that a lead-free solder joint is even more reliable than the equivalent tin-lead joint.
Rework or repair
Repair or rework should also be carried out using lead-free solder. It is necessary to be sure which solder has been used before attempting to rework it. Alloys used in lead-free solder can vary depending on the application, but it is generally felt safe to use tin-copper for lead-free hand soldering.

Q: What are the attributes of tin-silver-copper alloys?
A: Following in-depth industry research, the tin-silver-copper family of lead-free alloys has demonstrated the following attributes:
o Sufficient supply
o Adequate wetting characteristics
o A lower melting temperature than tin-silver or tin-copper
o A good fatigue resistance
o Good overall joint strength It appears that many manufacturers in the components industry are accepting these alloys. Tin has a relatively low melting point, copper is soluble in tin and is in plentiful supply, as is silver, which is also less cost prohibitive than other lead-free alloys when used in minimum quantity

Q: Is it true that pure tin terminations can exhibit some kind of growth characteristics?
A: This is well understood in the metallurgy world, and is often referred to as "tin whiskers". Under certain temperature and humidity conditions, microscopic whiskers can grow to several hundred microns in length. Tin whiskers are single crystal, electrically conductive, hair-like structures that grow from lead-free, pure tin surfaces. It is possible, in high-density PCB assemblies, for these whiskers to cause electrical short circuits, causing concern for makers and users of high reliability electronic systems that employ components coated in tin. Space, missile and medical are just three applications to witness the impact. Considerable research is taking place on the causes and prevention of tin whiskers. Texas Instruments, for example, use Nickel / Palladium / Gold on their packages with leads / pins, therefore avoiding the problem of tin whiskers

Q: RoHS - what is the approach on part numbering?
A: For customers across Europe and Asia Pacific on what is a matter of great concern. Some would like all codes to change while others request no change at all. However, manufacturers approach reflects the views of the majority of customers.
1. Where a manufacturer introduces a new compliant version of a product and decides to change their part number, we will sell the product under the manufacturer order code.
2. Where there is no change to the functionality of the product, and it can be soldered at the higher temperature required by lead-free solders, manufacturers will generally be keeping the same part number. In this instance we will not change their order code.

Q: How does lead-free solder react?
A: The lead-free solder has a much higher melting point than standard leaded solders, which was proven by setting the soldering iron to 220°c and trying to melt a test piece of solder. Once the iron was reset to 340°c the solder performed well giving clean joints, although the solder did not flow as easily as the normal leaded solder, this was probably due to the extra heat needed to be transferred from the iron tip to the joint. This may be more of an issue with finer point soldering tips with lower heat capacity than a medium or large sized tip.
Stranded test wires were tinned successfully and soldered to a test board without issue. Some wire insulation may melt if the iron is held onto the joint for too long while trying to get the joint up to temperature - this could happen whilst using lower powered soldering irons. Enameled copper wire was successfully tinned and soldered. SMD components were soldered into place, but the solder didn't seem to flow evenly around the components as well as the lower temperature leaded solder. A test PCB with leaded solder joints was successfully reworked using lead-free solder. A point to note is that when the two different types of solder are mixed, the appearance of the joint has a marked dull appearance instead of the usual shiny metallic finish. This may be giving an indication that the quality of the joints with mixed technologies are not as good. A comprehensive range of lead-free solders can found at www.kester.com

Q:Using a high melting point (90/10 Pb/Sn) solder for hierarchical soldering. What is the replacement for this lead-containing solder?
A: No suitable alternative has yet been identified for this solder which melts at around 302?C. This lack of an alternative has been recognised by the authorities, with the result that "lead contained in high melting temperature type solders" (i.e. tin-lead solder alloys containing more than 85% lead) has been added to the list of exemptions within the WEEE/ROHS Directives. So, until further notice you can continue to use this particular lead-containing solder.

Q: Do we need to change our inspection criteria and procedures for lead-free product?
A: Probably, but only in minor ways associated with the appearance of the lead-free joints. Example, lead-free soldered joints are less shiny and more uneven than their traditional counterparts, and the pcb land/pad coverage tends to be lower giving rise to copper halos. However, neither appearance seems to degrade joint reliability. You may have to alter the settings of your inspection techniques, manual or automatic, to take account of the reduced contrast associated with the reduced lead content.

JEDEC standard for measuring Tin Whisker growth