Put simply, why do some diodes such as most Zeners and Schottky diodes have a glass package as opposed to the more traditional plastic package?
Is it ease of manufacturing, thermal properties, or some other electrical phenomenon?
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10\$\begingroup\$ So you can watch the current flow by. \$\endgroup\$– Olin LathropSep 19, 2016 at 16:20
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\$\begingroup\$ If you have enough current going through your diode to be able to see the current the packaging is probably irrelevant. \$\endgroup\$– HugoagogoSep 20, 2016 at 8:16
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2 Answers
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Early semiconductor diodes were mostly glass packaged which provided the advantage that they were hermetic and did not depend on passivation of the chip to survive heat and humidity. The glass package also allows a very high operating temperature. Early devices such as the 1N34A (germanium) and the 1N914 as well as the 1N7xx Zener series became very popular and inexpensive.
Plastic-packaged devices were developed to reduce costs where high performance was not so important.
For example, the glass 1N4148 has a maximum junction temperature of 200 °C compared to only 150 °C for the plastic-packaged 1N4001.
Ceramic packaged diodes have also been produced.
answered Jul 28, 2014 at 4:42
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3\$\begingroup\$ One think to look out for with glass packaged diodes is their light sensitivity. \$\endgroup\$ Jul 28, 2014 at 13:38
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3\$\begingroup\$ I've never had issues with 1n4148's. (I just stuck one under an incandescent bulb with DMM measuring current, I got ~30nA right at the resolution limit of my meter so a bit suspect, but I'm pretty sure it's real.) (I'm too lazy to pull out the big guns.) I've had the biggest issue with (20V) Zeners that I use in a noise source. I run those right near the knee, and light will just kill all the lovely noise spikes. There the bias currents are in the 1-10 uA range. I'm not sure why the zeners seem to be more sensitive. \$\endgroup\$ Jul 28, 2014 at 13:55
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1\$\begingroup\$ I second the realness of light sensitivity, though it is a very small current indeed and significant in only the most sensitive circuits. LEDs make decent photodiodes in a pinch, and I bet (though it's just a guess) that a Zener operating close to the knee shares some mechanism with an avalanche photodiode. \$\endgroup\$ Jul 28, 2014 at 18:48
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1\$\begingroup\$ @PhilFrost Reportedly a flash photo of an old-style EPROM-based microcontroller (the kind with a quartz window for UV erasure) could cause it to latch up and be destroyed if it was powered at the time. \$\endgroup\$ Jul 28, 2014 at 18:54
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1\$\begingroup\$ The issue of flash photography and silicon components hasn't gone away completely: raspberrypi.org/blog/xenon-death-flash-a-free-physics-lesson . I guess the lesson here is don't use bare silicon dies without enclosures. \$\endgroup\$– Jack BSep 19, 2016 at 17:12
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Thermal properties. The glass and the semiconductor expand and contract at the same rates. This is for reliability of signal diodes. The expansions or contraction at different rates would cause damage to the semiconductor.
answered Jul 28, 2014 at 4:32
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2\$\begingroup\$ CTE SiO2 = 5e-7, Si = 2.6e-6. In what sense of "Matching" are these the same? \$\endgroup\$ Jul 28, 2014 at 4:54
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\$\begingroup\$ Sorry, some clarification and some history: electronicdesign.com/archive/… The glass used was of a molecular structure like pyrex. \$\endgroup\$ Jul 28, 2014 at 4:59
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\$\begingroup\$ That is from 2001, glass diodes were the first packaging type. So this link is doesn't support what you think it does. \$\endgroup\$ Jul 28, 2014 at 5:03
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\$\begingroup\$ I must be misunderstanding your comment. I was responding to the thermal expansion difference of the glass used in the process. That is all I was trying to support. \$\endgroup\$ Jul 28, 2014 at 5:07
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1\$\begingroup\$ The paper Is from October 25th 1961. The hypothesis did contain a "may" but the last paragraph states: No devices failed in five months. Diodes tested under 20-V reverse bias and similar environmental conditions did not show any changes after two months of testing, according to IBM researchers." Summing up the results. \$\endgroup\$ Jul 28, 2014 at 5:21