4 MB memory unibus/qbus card (was Qbus split I&D?)
paulkoning at comcast.net
Thu Mar 19 11:52:56 CDT 2015
> On Mar 19, 2015, at 12:30 PM, Jon Elson <elson at pico-systems.com> wrote:
> On 03/19/2015 09:29 AM, Paul Koning wrote:
>> I used to think of BGA as not possible for home construction. Then I read a nice article — https://www.beta-estore.com/download/rk/RK-10001_76.pdf — about reflow soldering using what amounts to a toaster-oven with a temperature control added, which apparently does the job just fine. There are some details to get right, which the article explains.
> I reflow boards in a modified toaster oven, not too different from the one in the picture. But, it did NOT work well when I first tried it. I just hung the thermocouple in the air, and the boards were burnt to a crisp! The IR from the heating elements is absorbed VERY well by the boards, and they heat much faster than the air. So, my trick is to poke a
> very tiny thermocouple into a plated through-hole in the board, and then it reads the actual temperature of the board. I still have some problems with hotter and cooler areas of the oven, but you can usually find a good compromise.
Nice solution. Yes, that’s the main detail the article mentions: the sensor has to be in a spot that has similar IR response as the actual board. The solution used in the article is to use a spare (blank) board for a reference. A different board with similar ratio of copper to etch should also work. Your solution is elegant if there’s a suitable spot you can arrange.
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