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TJ McDermott
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Blogger
Re: Planned obsolescence: A real design approach
TJ McDermott   1/26/2012 11:02:40 AM
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The cell phone industry takes forced obsolescence to a new high.  They've convinced us to accept a 2-year life on phones, trained us to salivate impatiently when the next generation arrives, without ever perfecting anything.  The phone you have now will not be supported in a year, will not receive updates to fix known bugs.

Rob Spiegel
User Rank
Blogger
Re: reflow RoHS solder?
Rob Spiegel   1/26/2012 11:01:42 AM
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Thanks for the report, Keith. In addition to lead, gold and silver also inhibit the growth of tin whiskers. But you can imagine the problem with using gold or silver. One of the big questions that remains is how effective nickel is. Some say it's great, some say it's not. Most of the electronics industry seems pretty comfy with non-leaded solder. Military and aerospace are still exempt from RoHS.

Charles Murray
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Blogger
Re: HP Printers and life
Charles Murray   1/25/2012 7:54:34 PM
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BobGroh: I concur. The only time I ever bought an expensive printer, it was no longer state-of-the-art after two years. I've had very good luck with inexpensive printers, and I plan to keep it that way.

KeithH
User Rank
Iron
Re: reflow RoHS solder?
KeithH   1/25/2012 3:55:51 PM
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Rob,

I am not an expert, just an interested witness to this 'RoHS solution' party.    Tin whiskers are not a recent phenomena, they were first noticed back in the 1940's. 

If you are really interested, you need to read this NASA report.  It is quite an article about how whiskers can materialize within days or weeks.  They can start, stop and then resume for no known reason. 

That is the problem - there is no means of determining when or where they will occur as the cause is unknown - just be assured they will develop.  Thankfully most do not cause a major issue and infrequently significant damage.    Voltage does impact the presence (growth) but NASA claims they develop in vacuums, which eliminates most arguments for what we can do to prevent them.

The most serious implications are that they will penetrate conformal coatings - the only assured method to prevent it appears to be that adding Pb inhibits the growth, again the reason is unknown. 

http://nepp.nasa.gov/whisker/reference/tech_papers/2011-kostic-Pb-free.pdf

KeithH

Rob Spiegel
User Rank
Blogger
Re: reflow RoHS solder?
Rob Spiegel   1/25/2012 3:19:21 PM
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Keith, it is my understanding that tin whiskers form long after the product is completed, shipped and in use. Typically they form when the solder is under stress, which makes the problem most common in military and aerospace applications. At least that's when I've seen in NASA reports.

KeithH
User Rank
Iron
Re: reflow RoHS solder?
KeithH   1/25/2012 1:18:25 PM
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350 F should remove tin whiskers as the melting point of tin particles is 177 C or 350 F.  Tin Whiskers range in size from 6 nm to 10 um - well within the specification of a tin particle.  Besides, 'normal handling' of a PCB will break the whiskers as most individuals do not handle PCBs properly outside of the industry and they cannot 'see' the root cause.

Rob Spiegel
User Rank
Blogger
Re: HP quality
Rob Spiegel   1/25/2012 1:12:50 PM
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I've had problems with an HP printer I purchased about 4 years ago. I finally gave up on it. My guess is the quality problems coincide with outsourced manufacturing.

Bryan Goss
User Rank
Gold
List of what can't take the heat of baking?
Bryan Goss   1/25/2012 12:57:03 PM
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I have been fighting a problem with Mitsubishi PLCs model FX2n. They were built about the time RoHS was first being implemented. I have about 300 of them on machines around the country, and so far 5 of them have lost their minds, each in a different way. One started making addition error. Another kept changing the value of one of the customer input data. Another kept changing several of the values of battery-backed parameters. Etc. Mitsubishi is no help, all they say it that it can't be doing it or it must be my programming of it. Of course they can't explain why I have 295 out there with the same programming that work fine, or why these worked fine for years.

So I am very eager to try baking one of these, and see if that fixes it. However, I am not sure what parts can withstand the heat of baking. Does anyone have a list of things that can't be baked?

 

npitech
User Rank
Iron
reflow RoHS solder?
npitech   1/25/2012 12:28:22 PM
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Most lead free solder used in electronic production melts around 220C (428F) and reflow temperatures are slightly higher. I have to doubt that a 350F oven fixed a lead free solder problem.

D. Sherman
User Rank
Silver
Re: HP Printer life
D. Sherman   1/25/2012 12:05:07 PM
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Most likely the baking helped with either a moisture/conductivity problem, or with a thermal intermittent. Two problems in PCB manufacturing came along at almost the same time -- the switch to brittle, lead-free solder, and the switch to water-soluble flux. I've seen problems caused by both issues that could be "fixed" by baking.

If you have a cracked solder joint, the only permanent fix will be to find it and re-solder it with good solder. Typically, it's heavy components with large tabs that have the soldering problems, both because the thermal mass of the heavy part tends to result in a cold solder joint under the best of circumstances, and the weight of it exacerbates any vibration or thermal expansion problems, which can crack brittle solder. An engine control relay module in ~1990 Honda Civics was notorious for that.

If conductivity is the issue, if the device is kept in a warm dry environment henceforth, it may be fine. If not, the best solution is to scrub the board with warm, soapy water and a soft brush, blow it dry with clean air, bake it to drive out remaining moisture, and if operation over a wide range of temperature or humidity is expected, spray both sides with two thin coats of a conformal coating. Ordinary clear acrylic enamel can be used, but I prefer the silicone coating for its flexibility.

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