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Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
Yes it does. ESD is very important. We constantly have issues with ESD deniers busting stuff that's meant to go to customers. I shall bite my tongue here to prevent a long rant ... The humidity stuff isn't usually such a problem, but you really shouldn't let parts absorb water - it can lead to 'pop-corning' during soldering. More of a problem in mass production as it affects yields. Still best to leave your parts sealed in the bag with the dessicant until you need them. As an example: some years back a place I worked for wasn't too careful with storage. There were some big smt ceramics in one of the designs (1uf) that had sat in an open pack for some months before being used. During soldering the absorbed moisture turned to steam an created micro-cracks in the dielectric. This didn't result in instant destruction of the caps - what happened is over time a process called electro-migration gradually formed shorts through the cracks leading to milliamps of leakage, in a product meant to last 6 months on a single battery charge. Not good. Lesson learned.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
2Spoons wrote ...
Yes it does. ESD is very important. We constantly have issues with ESD deniers busting stuff that's meant to go to customers. I shall bite my tongue here to prevent a long rant ... The humidity stuff isn't usually such a problem, but you really shouldn't let parts absorb water - it can lead to 'pop-corning' during soldering. More of a problem in mass production as it affects yields. Still best to leave your parts sealed in the bag with the dessicant until you need them. As an example: some years back a place I worked for wasn't too careful with storage. There were some big smt ceramics in one of the designs (1uf) that had sat in an open pack for some months before being used. During soldering the absorbed moisture turned to steam an created micro-cracks in the dielectric. This didn't result in instant destruction of the caps - what happened is over time a process called electro-migration gradually formed shorts through the cracks leading to milliamps of leakage, in a product meant to last 6 months on a single battery charge. Not good. Lesson learned.
I only meant moisture, I have had to deal with static all the time on many different components for 20+ years, but rarely dealt with moisture sensitvity.
I seem to be finding 168 hours or 4 weeks for a 2a moisture level out of the bag, though this is a conflict with other sources. As 28 days equals 672 hours, not 168... I guess ill just be sure to complete soldering today or tommarow then?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Wooooo Hooooo!
this pic shows what was attempted and the result. From the top of the shiny paste location to the bottom paste location is 0.360 inches, about half is shiny and now solid.
Remember this was a test of thermal conduction, as the soldering iron was about 0.062 inches away from the nearest paste.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Nice picture of nice result, Patrick.
+1 on what 2spoons said. Board assembly managers take very seriously the environment and shelf life of unbagged components. Consider the rate of defects when a product has 1000's of components and 10000's of reflowed connections.
Absorption of moisture can often be mitigated by (scientifically) baking out the parts. But how about oxidation / corrosion of terminal surfaces, which were originally solder-friendly. Or should I say, in the ROHS era, not intolerably solder-unfriendly ?
Most of the bare boards at my workplace are ordered with a very thin layer of gold on all non-solder-masked surfaces. That's good for shelf life in the stockroom, before assembly. The gold layer must NOT be too thick, because it entirely dissolves into the solder during reflowing. Doesn't take much gold to mess up the properties of the solidified solder.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
but im still trying to get to the bottom of the 2a categorization. what does that really mean? 6 minutes or 600 hours out of the back before moisture kills it?
my bags say 168 hours and 4 weeks, but both bags are 2a...
im too tired to continue, I have a real nice SMD LED test circuit to be etched, but I forgot Brother toner isn't PCB capable, so I have to get my HP laser printer out in the morning...
EDIT: I just lit up my royal blue-ish LED, really bright, really blue. not pale cyan like those crappy radioshack blue leds... ill post the super bright R,B,G,Y LEDs as soon as I get the board etched...
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Im trying to get my HP 1102W laser printer working, its just printing all black pages.
supposedly there are two springs cuasing the problem. problem is caused by lateral springs (the ones with U shape) that do not touch the lateral contacts on the toner!whatever that means... this is the only printer I have capable of printing transfers. if I cant get this to work im screwed.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615
Patrick wrote ...
but im still trying to get to the bottom of the 2a categorization. what does that really mean? 6 minutes or 600 hours out of the back before moisture kills it?
my bags say 168 hours and 4 weeks, but both bags are 2a...
From memory, most parts are fine for a couple of weeks out of the bag, unless you are in a really humid environment. Industrially the store rooms are generally air-conditioned, and humidity controlled.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
thank you 2spoons.
right now I guess im going to take apart a HP p1102w laser printer to try and fix the corona wire... I don't even know if its in the printer or toner cartridge. Brother printers are totally different, and in my experience totally superior.
I wonder if HP toner can be put in a Brother printer? im not brave enough to ruin two cartridges and possibly my better brother printer. Or better still -- have a remanufactured brother cartridge filled with normal toner, compatible with transfer paper...?
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Low Melting Point (281F) Sn/Bi Solder for SMT.
