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Unforseen issue with hot-plate reflow

Really, the primary driver of the choice was (a) because I seem to get a balance of recommendations for toaster ovens and skillets, (b), because the Goodwill store was on my itinerary before Target, and (c), because the Goodwill store didn't have any toaster ovens that looked decent!

So, it was a hugely sophisticated decision process. I figure that for $5 I could try it, and just run out and buy a toaster oven and start messing with it if need be.

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Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott
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There is no solder paste on the bottom of the board, and have you ever tried soldering to stainless or even worse aluminium? you need very clean metal and aggressive fluxes

-Lasse

Reply to
Lasse Langwadt Christensen

Way to practical...you will never succeed in management...

Reply to
Bill Martin

Some of the cutting fluids have a really rank smell. Not that I like the smell of ethanol that much better, but it would dissipate faster.

**Pure** ethanol is not nice stuff (from a student safety manual):

"There is a serious risk of liquid catching fire; its vapour may catch

19% ethanol). Breathing vapour may result in sleepiness: the concentration in the air should not exceed 5760 mg m-3."

Just what you need when generating hot swarf and hovering around metalworking machinery..

Reply to
Spehro Pefhany

Oh, it has a tendency of making people merry. ;-) One marvels at the precision of the maximum allowed concentration figure. A lot of research must have gone into that.

Yohoooo!

Jeroen Belleman

Reply to
Jeroen Belleman

Den fredag den 13. marts 2015 kl. 15.55.41 UTC+1 skrev Spehro Pefhany:

you only need two drops to drill a hole not a big issue

-Lasse

Reply to
Lasse Langwadt Christensen

I tend to ignore recommendations, advice, and promotions, but do respond to discounts, sales, bribes, free samples, and convenience. In other words, I'm cheap and lazy. I was going to say something derogatory about shopping at Goodwill, but must confess that the local Goodwill store has a half-off on electronics day, where I can usually pickup bargains that I don't need. This week, it was a 1600x1200 Dell monitor for $5 and three new ADSL2+ modems for about $10. Therefore, shopping at Goodwill meets my approval.

When you tired of the greasy spoon smell on your PCB's, Target also has the bottom of the line toaster oven for about $25.

I have a house and office full of junk that was purchased using the same logic.

While this is a bit off topic, I did make some interesting observations using the B&D toaster oven to do BGA reflow repair. This does NOT apply to solder paste reflow.

  1. The BGA solder balls melt at a much lower temperature than the solder paste. Therefore, the only things of importance are to target the temperature not to approach the solder paste temperature and to maintain the temperature in between the two melting points.
  2. A proper solder temp profile is impossible with such a crude oven. However, a crude ramp up in temperature can be achieved with a thermocouple temperature sensor on the PCB, and a timer.
  3. Despite recommendations on the printer repair sites (i.e. FixYourOwnPrinter.com) of 6-8 minutes, I found that 10-12 minutes works better. Most of my initial failures were from too short an interval.
  4. I need to install standoffs on the PCB to prevent contact with the grill and drip pan.
  5. I didn't need to reflow the circuit side of the PCB, so I left the lower drip pan in place.
  6. Opening the oven door is good for a huge drop in temperature. I pre-heat the oven to roughly the target temperature, quickly open the door to insert the PCB's, wait for the temperature to climb back up, and then start the timer. For cool down, I just turn off the oven power, wait for the temp to drop a little, open the oven door slightly, let it cool down to handling temperature, and then fully open the door. Using the door as a temperature regulator is rather crude, but I had 14 JetDirect cards to fix and I didn't want to spend all day doing it. All this is possible because the oven has a low thermal mass and does not take very long to heat up or cool down.
  7. The glass door is hot. Have burn grease handy.

Unfortunately, my system is not infallible. I tried to reflow an HP laptop motherboard, which didn't work. I plan to try again, this time slopping some flux on the BGA chip(s).

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

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