Quote:
Originally Posted by williamson
Mr. Smalls is absolutely right. We have 100 years of technicians soldering, and I've never heard of one getting lead poisoning.
|
I'm sorry, but that doesn't sound like the sort of argument an engineer makes. Perhaps you are speaking from the point of view of a manufacturing technician?
The primary problem with leaded solders is measurable, direct risk to workers in manufacturing, not secondary risk from waste. That latter exists, but exists with many, many compounds, which is why waste management engineering has to take other steps to prevent exposure and contamination of groundwater, etc.
The danger to workers is measurable, and still of concern in exempted areas of aerospace and the military (ex. see the recent UC Davis study and the work of the JG-PP (see below)). That is, folks working with leaded solder are at statistically higher risks for lead related health problems.
In design engineering, we look at larger statistical samples. That is, making one run on the bench is not the same thing as predicting reliability of 1,000,000 in the field. Also, you are required to account for spectral factors. Severe heavy metal poisoning results in some very obvious symptoms, incoherence, impaired memory, neuromuscular problems, etc. But smaller doses often result in statistical correlation to more subtle problems, or serious problems over a much longer period of time.
This form of statistical-universe-of-one-as-'obvious' argument is a very human reaction. I'm tempted to go over a photo someone sent me recently of a book in a snowdrift, but that is too politically charged, so let's take alum. Aluminum salts are the most common metallic element on earth - the third most common element in the earth's crust overall, so there is no particular reason to suppose that we are not exceedingly well adjusted to it. But alum toxicity, as well as causal relationships to serious long term ailments like alzheimer's disease are quite real. In fact, we add small amounts of alum to some vaccines to trigger a severe immune system response in the human body.
But how should we react to this knowledge? Humans are, instinctively, highly reactionary and subjective creatures. So, the most two common reactions are: 1) panic and be terrified of alum. cookware and products like deodorants (both of which the FDA has deemed to generally safe) or 2) interpret the singular absence of immediate and obvious harm as a definitive proof of 'safe' (ex. "Well I eat Jiffy Pop and I don't become incontinent and yell at clouds, so it must be a load of hooey...") Either way, the instinctive, or emotional reaction has no logical relationship to objective risk assessment and management.
Quote:
Originally Posted by williamson
Each person viewing this site will have to decide his own priorities, when it comes to lead-free.
|
If they live here in CA with me, I sincerely hope not. I don't get to pour mercury or MTBE down my ground drain and I don't have to look much beyond the crowd at the airport or current primetime TV to make the case that vast numbers of my fellow citizens are not properly equipped to make intelligent decisions about public heath and environmental toxicology on an individual basis.
Quote:
Originally Posted by williamson
This site is called "a reliable". As stated earlier, the military doesn't allow it because of "wetting". So if you are inexperienced in soldering, you should take into account that lead-free may not "wet" as well.
|
The DoD and NASA both participate in something called JG-PP, the Joint Group from Pollution Prevention. JG-PP and JPL both have done studies on the implications of lead free versus leaded solder. There is also a report from the JC-AA (Joint Council on Aging Aircraft), but that is really just a summary of the JG-PP '06 and '07 study reports.
The super short summary is that solder joint reliability turns out to be a lot more complicated than leaded vs. unleaded solder. Lead free compounds appear to be just as reliable in many applications. In those that the joints fail, it isn't generally a deficiency in the solder compound so much as a systemic (design or total material) or a manufacturing problem (remember, it is generally unleaded solder being directly substituted into existing designs and manufacturing processes).
The JPL study is interesting in that it didn't just look at subsystem reliability, but failure based on application technology. Hand soldering had the smallest discernible difference in reliability (essentially zero in industrial temperature range applications). On the flip side, hand soldering represents the highest exposure and statistical risk to the workers.
So, with no disrespect to your personal experience, I can't find any evidence from the military and aerospace studies to support the idea that hand soldered lead free boards are not reliable in consumer automotive applications.
Remember, the military definition of 'reliable' and the common understanding are two different things. A brand new commercial airliner is not reliable enough for military applications, even though it uses lighter and stronger alloys than a mil spec aircraft. The modern nav system in the plane I most often fly is lead free, as are the ECUs and brake module in my daughter's car, and I'll never lose a moments sleep about either.
Consumer electronics are highly sensitive to changes in reliability. Because of the margins, a warrantee repair is catastrophic to the bottom line. Following the work and articles on statistical quality control, consumer manufacturers have, by and large, found the move to lead free fairly smooth.
Automotive applications have some other challenges, but I'd readily bet good money that, say, Toyota's current woes have everything to do with designs and firmware, and nothing to do with the type of solder.
-jjf