LEAD-FREE
FREQUENTLY ASKED QUESTIONS

COMPONENTS

Do the component terminations have to be lead-free?

Component terminations, the surfaces being soldered, must be lead-free. The solder spheres for ball grid arrays must also be lead-free. Internal solder used for construction of the component can contain solder with more than 85% lead.

What lead-free finishes are alternatives for tin-lead finishes?

Component terminations are more consistently solderable if they are pretinned with melted solder. Alternative lead-free solders for tinning are tin-silver-copper, tin-silver, tin-copper, and tin-bismuth. Other metals can be plated onto the terminations, but the same potential problems exist as with printed wiring boards. Component manufacturers seem to have mostly standardized on matte tin plating or palladium-nickel. Electroless nickel under immersion gold is acceptable provided the nickel does not contain more that about 7-8% phosphorous.

What problems might be anticipated with lead-free components?

The main problem is the same as existed with tin-lead coated component terminations, dewetting or nonwetting during soldering. Tin can be plated onto the termination even though the surface being plated is not solderable. Gold and palladium dissolve rapidly into the solder, so the nickel underneath the precious metal must be solderable.

What are the changes in reference to lead-free assembly in the J-STD-020C, dated July 2004?

The IPC/JEDEC J-STD-020C, issued July 2004, entitled Moisture/Reflow Sensitivity Classification for Non-hermetic Solid State Surface Mount Devices details the thermal profiles SMD components must meet to be classified as lead-free process capable.

Higher thermal profiles with lead-free in the range of 235-255º C, may require component re-qualification to new moisture sensitivity limits. This needs to be known and adequate measures taken to avoid moisture issues such as popcorning, delamination and cracking issues during lead-free reflow.

This document is also useful to procurement, where lead-free components can be referenced to the requirements set in this standard.

Can I solder leaded components in lead-free wave soldering?

Leaded terminations cannot be soldered in a lead-free wave solder process. Lead-free solder bar will have a small amount of lead when received usually in the range of 0.01 to 0.08%. The RoHS Directive states a maximum of 0.1% lead; it does not take very much lead to surpass this limit. To avoid surpassing this limit, leaded terminations should not be allowed. There is no effective way to reduce lead content except by dilution if lead were to go beyond 0.1%.

Also lead contamination can be a contributor to fillet lifting and fillet tearing. Although this is not considered a defect as per IPC-610D, further studies are required to determine the impact on high reliability assemblies. For consumer electronics reliability would not be an issue since most are not exposed to thermal cycling or thermal shock during their use.

Can I solder reliably leaded terminations with lead-free solders in an SMT process?

The amount of lead on SMD terminations can be small often component manufacturers will use 10/90 or 15/85 for the tinning. A small amount of lead will be introduced into the lead-free joint and for small amounts of lead under 2% by weight this doesn’t impact the pull and shear force results when tested. Some assemblers have used a mixed bag of leaded and unleaded SMD’s with no impact to product reliability. Most are in consumer electronics.

For the highest reliability a complete lead-free system is preferred. If leaded SMD components must be used, it is recommended to access product reliability and therefore some testing may be required.

An important note to that for RoHS compliancy lead must be kept below 0.1% in the joint also, lead in terminations may impact this negatively.

Can I solder lead-free terminations with leaded solders such as 63/37?

Lead-free terminations such as pure tin, silver palladium and tin bismuth have been in use for years. So they are already being soldered with 63/37 solder without much issue.

Today more and more components are coming lead-free, where they may have had a leaded finish before. Some component manufacturers are issuing different part numbers some are not; some companies are notifying distributors and assemblers of the change some are not. For the assembler, even if it is not going to lead-free soldering, it becomes important to know what these new finishes are since solderability may change requiring process optimization to maintain product reliability.

How can I check if my components supplier has really delivered lead-free components?

This can be very difficult as not all component suppliers will change part numbers of the components. Some suppliers do mark packaging with some kind of Lead-free symbol. If in doubt some analytical methods exist. These can be destructive or non destructive.

A non destructive method is to wipe the component lead surface with a cotton bud, place the bud in a reactive chemical. If Lead is present the chemical will color pink to read. The destructive methods consist of SEM/EDX, ICP or AAS measurements.

Is there a universal marking available that can be put on the assembly indicating RoHS compliance and/or Pb-free?

No there is no such universal marking. The RoHS directive does not require any marking of final assemblies. The Soldertec institute and IPC have some advisory guidelines on marking. These can vary from symbols such as crossed out Pb in a red circle to a diamond with RoHS in black letters. A common symbol for the PCB would be the letter e with a number. Each number will indicate an alloy family. No marking would indicate SnPb.

More info on www.ipc.org or www.soldertec.org

How do I ensure that no mix-ups between LF and non-LF soldering materials will occur in the production floor?

A complete inventory list of all current materials should be conducted and the items should be clearly labeled and identified. The production lines should be well dedicated and segregated for leaded and lead-free to avoid any risk of cross-contamination.

Kester's lead-free soldering products are easily distinguishable by the use of different packaging colors for paste and shapes for solder bars. This has helped the customer in implementing a total lead-free solution.