Pluses and Minuses of Pb-Free Solder


I thought I would take a stab at listing the minuses, pluses, and “it’s a wash” aspects of assembling with lead-free (LF) solder. Here are my first thoughts. Please tell me what I missed or disagree.


1.    Pb-Free requires higher reflow temperatures
The Tm for LF solders, in the 217-229C range, has created numerous challenges:

a.      PWB warpage and damage

b.      Component damage

c.      New defect modes such as graping and head-in-pillow defects (although concurrent reduction in solder paste deposit sizes for 0201 and 01005 passives and 0.3 mm CSPs also exacerbate these defects)

d.      Defects related to increased oxidation

e.      Increases in voiding

f.       Increases in tombstoning

2.      The higher cost of LF solder, mostly for wave soldering

a.      It’s not just the silver, tin is much more expensive than lead

3.      Poorer wetting of LF solders, creating the most significant challenges in wave soldering

4.      More rapid copper pad dissolution on PWBs in wave soldering

5.      LF solder attack of wave solder machine components

6.      LF reliability in harsh thermal cycle testing appears poorer than SnPb solders

7.      Tin Whiskers

It’s a Wash

1.      Short-term reliability in consumer product-type environments

2.      Protection of the environment if discarded products are improperly disposed of

a.      Lead in electronics has never been shown to cause a problem in land fills

3.      Since July 2006, about $3 trillion of products have been manufactured with LF solder, with no “the sky is falling”-type of problems


1.      LF solder’s poor wetting enables finer lead spacings (see photo courtesy of Motorola)

a.      It may be argued that some modern electronic products (e.g., smartphones) could not be made with SnPb solder

2.      It is safer to recycle LF solders, especially if performed in a non-controlled environment
OK — your turn. Please comment.

Best Wishes,

Dr. Ron

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About Dr. Ron

Materials expert Dr. Ron Lasky is a professor of engineering and senior lecturer at Dartmouth, and senior technologist at Indium Corp. He has a Ph.D. in materials science from Cornell University, and is a prolific author and lecturer, having published more than 40 papers. He received the SMTA Founders Award in 2003.

5 thoughts on “Pluses and Minuses of Pb-Free Solder

  1. Minuses #7, tin whiskers, should be #1. And, It’s A Wash, #3 is in doubt. NASA just released a study of unintended acceleration and found tin whiskers. Although they absolved Toyota of any responsibility, the lead free issue may have unintended consequences. Not sure how safe the cars are since tin whiskers are so unpredictable. Personally, I think the airline, medical and auto industries should get waivers for lead free. It does not bother me if my I-Pod dies after a couple years due to tin whiskers, but I don’t want to go down in an airplane, operating table or out of control car… It could be the other guys car, too.

  2. Totally and precisely agree with D. Zirkelbach. In aviation, especially safety and emergency devices in this sector, eliminating risk is the only way to fly. The European community still gives exemptions (negotiated buy off) to lead in car batteries, so get off my back about the fractional ounce in SMD boards.

    Take a close read on the NASA, Boeing, and others’ reports on tin whiskers, and simply say “No thanks.” If electronic products are simply made consumer tamper-resistant, the exposure to contacting lead is merely rhetorical. Get real.

  3. I agree with Messrs. Zirkelbach and Haas. In addition, from a recent report from the ACI, in Philadelphia, intermetallic growth between solder and the pad is more extensive which may make the incidence of intermetallic fracture more extensive (still under study). Also, the order of environmental fatigue testing, affects the solder’s performance. Fillet lifting can occur with lead fee solder, and the ability to “self-align” is compromised due to the poor wetting. Because of Pb-free’s more brittle nature, probe testing that can bend the board can induce solder damage. On the plus side, gold embrittlement seems to be reduced.

  4. Many good points (pro / con)
    but I agree with the others above..

    According to representatives from large distributors…
    Market forces have forced most Military and some Aerospace companies to go ROHS…
    People in general.. expect Military and Aerospace to be MORE complex/ high tech than consumer goods.
    And the semiconductor industry will not supply two or more versions of their products… it seems , regardless of $ incentives possible by these industries.

    Which leads to the electronics industry not supporting two flavors (lead and non-lead), regardless of what the law allows.

    and if we go “all in” with ROHS ….. more people die (than if we stayed with lead)…
    reason: mission critical (life dependent) products will become less reliable.
    Military, medical, aerospace, infrastructure (power/telecom)..all with higher risks.

    This leads to electronics becoming equated to “not reliable / short lived”

    What does THAT do to the world’s economy?
    As pointed out.. consumer goods? obsolescence is expected.
    Mission critical goods? not acceptable.

    The sooner we learn.. the less it will cost (in lives and $) to extricate ourselves from ROHS and it’s ilk.

    I am all for being responsible with the environment.. but ROHS hasn’t been proven to be…
    just another well meaning , knee jerk reaction by people in positions of authority rather than a well thought out plan of action.
    in other words.. political not science based.

    Even 1-5% lead.. would eliminate the few Pluses mentioned for ROHS processes and still eliminate whisker issues.

    What ever happened to moderation?

  5. Pingback: Questions on Tin Whiskers at Circuits Assembly blog

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