The development of new environmental legislation such as the WEEE/RoHS directives has raised many concerns, especially with respect to the fact that lead will effectively be prohibited in most electronics put on sale in the European market from July 2006.

• These directives affect the Printed Circuit Board Manufacturing and Assembly Industries doing business in the European Union in several ways.
• By July 1 st, 2006, all electrical and electronic equipment “put on the marketplace” may not contain Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominatedbiphenyls (PBB’s) and Polybrominated Diphenyl Ethers (PBDE’s) in amounts exceeding the set maximum concentration values (MCV’s).
• For all electrical and electronic equipment put on the marketplace before AUGUST 13 th, 2005, the costs of waste management are to be shared by all the producers in existence at the time those costs are incurred.
• Information assisting companies to understand and achieve compliance can be found by visiting the following two (2) web sites. Copies of the actual Directives can be downloaded from 2.a.
• http://www.pb-free.info/
• http://www.ul-rscs.com/AS_home.aspx

LEAD FREE SOLDER CHOICES

There are many lead free solder alloys commercially available with a range of melting points, but those that are proving most popular for both reflow and wave soldering in Europe have melting points significantly higher than the tin lead solders they replace. This has important ramifications for the materials and components being assembled because higher soldering temperatures need to be used in reflow, wave solder and hand soldering operations. These higher temperatures mean changes to materials, equipment and processes. Coupled with the fact that lead free solders tend to behave different than tin lead solders, there are a number of important considerations that must be addressed if successful lead free assembly is to be achieved.

The importance of establishing a good dialog with your suppliers, but also with equipment manufacturers cannot be over emphasized.

Traditional electronic assembly relies on the use of Tin Lead based solders at 60% / 40% or 63% / 37% which melt at, or around 183 degrees C (365 degrees F approx.) Newer solders based on Tin-Silver-Copper alloy compositions, (also known as SAC alloys) are being widely used for both reflow and wave soldering. These alloys have a melting point at between 215 and 229 degrees C (415-446 degrees F approx.) For wave soldering alone, the Tin-Copper eutectic alloy (Sn-0.7Cu) melts at 227 degrees C (437 degrees F approx.) and represents one of the lowest cost lead free alloys available. Thus, for most European Companies switching to the lead free solder alloys, the key challenges have been the elevated temperatures and times required, and the role they play with associated PCB substrate materials and component metallic coatings.

SUBSTRATE LAMINATE MATERIALS

Due to these newer soldering temperatures, the materials of which the Printed Circuit Boards are made from had to change drastically as well. National Technology, Inc. (NTI) has chosen several new laminate versions that meet not only the elevated temperature requirements, but also the six banned chemical compounds as well.

These materials are:

These materials are all of the FR-4 based family of laminates and pre-pregs. Cost factors being seen are 5-30% higher when looking at Multilayer products to 200-400 times higher when looking at standard rigid Double Sided Plated Through designs / applications. Note: These values represent information collected through various sources and should not be used for solid costing factors. Verify actual cost with your printed circuit board suppliers.

ALTERNATIVE SURFACE FINISHES

Since Solder coating, i.e., Hot Air Solder Leveling, Hot Oil Solder Leveling, will no longer be a viable option as a surface finish, National Technology, Inc. is offering the following alternatives. Note: Cost estimates based on surface/through hole square inch area to be coated.

When making a choice on alternative surface finishes, the alloy replacement for tin lead solder and or solder pastes becomes of the upmost importance. Not all surface finishes are compatible with all tin lead replacement alloys.

Opening a line of communication with your PCB supplier as well as your component suppliers is key to the success of your transition to lead free compliance.

DESIGN / SPECIFICATION ELEMENTS REQUIRING THOUGHT

The thermal stresses the boards may see with alternatives to tin lead processing will not only effect the flatness of the PCB itself, but the plated through hole barrel also. Data from copper elongation testing performed by National Technology, Inc. on one ounce copper suggests that, with the elevated processing time and temperatures, the IPC minimum average thickness of .0008” plating in the hole wall may have the potential to stress and elongate manifesting in cracks.

Data from tests show that a hole wall thickness of ,.001”minimum to .0014” average, offers a more robust through hole. Due to Z-axis expansion of the board, caused by the longer times and elevated temperatures, the once acceptable minimum copper hole wall values may be prone to failure. As for general flatness, it is suggested that relief slots be utilized when ever possible on large array / pallet type designs. Copper thermal relief patterns in rails to add rigidity is also recommended.

On Multilayer designs, attention should be paid to balanced layer constructions, with copper cross hatching or “dots” used on all layer artworks whenever feasible, again to add rigidity to board through thermal cycles.

Opening a line of communication with your PCB supplier is key to the success of your transition to lead free compliance. Getting them involved as soon as possible in the design phase can save valuable time and dollars in the long run. These items are being offered as suggestions to preparing for the “lead free challenge” and are by no means to be considered all inclusive as to the intent of the European Union WEEE / RoHS directives.