Author Topic: Why are ICs/Semis black?  (Read 3931 times)

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Offline PStevensonTopic starter

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Why are ICs/Semis black?
« on: May 03, 2021, 11:34:59 am »

I was showing my young nephew some PCBs (trying to get him into electronics) and he asked me why are all of the square things black?
I just said that it's probably because it helps it work (light can mess with the operation) and that it's easier to print visible text on it.

but does anyone actually know why they're (mostly) black?
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Offline Brumby

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Re: Why are ICs/Semis black?
« Reply #1 on: May 03, 2021, 12:10:18 pm »
Light shining on a silicon die can affect operation of circuits.  Think solar cells.

EPROMs are a classic example where a clear window allows for erasure of stored data.  Photons can mess with circuit operation.

Black plastic or other opaque material (such as ceramic) block light.
 

Online newbrain

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Re: Why are ICs/Semis black?
« Reply #2 on: May 03, 2021, 12:20:55 pm »
Light shining on a silicon die can affect operation of circuits.  Think solar cells.
When the world football cup was hosted in Italy, in 1990, a brand new telephone xchange was installed close to the stadium.
Since it was quite an advanced (for the times) model, various foreign dignitaries were invited and shown it.
Every time an official visit was going on, a complete restart (an event that should happen at most 3 times in a year) happened.

After much head scratching, it was found that:
  • Journalists and visitors used flashes to take pictures
  • Some of the DC/DC boards were mounted on board extender, to show them off.

Well, on those boards there were some diodes, and they had a glass enclosure.
The flash light was enough to start an avalanche and kill the power for a short time.
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Offline G7PSK

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Re: Why are ICs/Semis black?
« Reply #3 on: May 03, 2021, 12:51:08 pm »
Red or brown and blue plastic would do the job but I think there are two reasons for using black plastic.
For a start it tends to be cheaper or at least in the past it was as carbon black is used to make the plastic black and that is cheaper than the plastic or was in days gone by second reason is in days gone by pitch was used for encapsulating electrical and electronics so black is familiar, in the 60's there were some transistors and other semiconductors in both red and blue packaging.
 

Offline NiHaoMike

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Re: Why are ICs/Semis black?
« Reply #4 on: May 03, 2021, 12:51:59 pm »
When the world football cup was hosted in Italy, in 1990, a brand new telephone xchange was installed close to the stadium.
Since it was quite an advanced (for the times) model, various foreign dignitaries were invited and shown it.
Every time an official visit was going on, a complete restart (an event that should happen at most 3 times in a year) happened.

After much head scratching, it was found that:
  • Journalists and visitors used flashes to take pictures
  • Some of the DC/DC boards were mounted on board extender, to show them off.

Well, on those boards there were some diodes, and they had a glass enclosure.
The flash light was enough to start an avalanche and kill the power for a short time.
Or more recently, a design flaw with the Raspberry Pi 2:
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Offline srb1954

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Re: Why are ICs/Semis black?
« Reply #5 on: May 03, 2021, 01:13:14 pm »
Light shining on a silicon die can affect operation of circuits.  Think solar cells.

EPROMs are a classic example where a clear window allows for erasure of stored data.  Photons can mess with circuit operation.

Black plastic or other opaque material (such as ceramic) block light.
Some opto-coupler devices are encapsulated in white plastic. Can anyone explain the reasoning behind that.
 

Offline beanflying

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Re: Why are ICs/Semis black?
« Reply #6 on: May 03, 2021, 01:36:12 pm »
Light shining on a silicon die can affect operation of circuits.  Think solar cells.

EPROMs are a classic example where a clear window allows for erasure of stored data.  Photons can mess with circuit operation.

Black plastic or other opaque material (such as ceramic) block light.
Some opto-coupler devices are encapsulated in white plastic. Can anyone explain the reasoning behind that.

Very likely voltage separation reasons. A lot of Optos are meant to isolate HV from LV DC so carbon black for example would reduce the distance.
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Offline T3sl4co1l

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Re: Why are ICs/Semis black?
« Reply #7 on: May 03, 2021, 01:53:22 pm »
Well, black plastic is rated for as much voltage as anything.  (In fact it's mostly silica fume, apparently earning a CTI category I rating, hence the minimal clearance on, for example, 1500V rated TO-220s.  And also hence the minimal expansion, allowing them to be soldered without failure, despite going over the glass transition temperature of the resin used.)

The white ones just have slightly higher CTR.  I suppose the opto capsule could just as well be layered with a white shell, then embedded in a regular black plastic package for the best of both worlds.

Optos BTW are usually made with, something like a silicone blob lens, between the emitter and detector, I think also with an explicit barrier such as a thin sheet of glass.  Of course it's not actually a lens because there's no air around it, or anything else of different refractive index (and useful shape); it's just that something has to fill space else the resin will.  So, with poor collimation, you would expect white resin to do better, though apparently not by much so it's neat that it performs as well as it does without much of a lens in there.


I've seen plenty of ICs in colors, but all of them old types (~70s?).

Heh which, I think one of them I remember was a buff or cream-colored 7404 made in the 6th week of 1974... or maybe it was a 7406 made in the 4th. :-DD

PNP transistors you sometimes see in green, for whatever reason.

I think I've seen some blue thyristors, though checking, I only have gray and black ones in my bin.

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Offline Yansi

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Re: Why are ICs/Semis black?
« Reply #8 on: May 03, 2021, 01:59:57 pm »
I think that the green marking of P-type semiconductors was some kind of Japanese standard? I have seen this green signature mostly or only with Japanese made components.
 

Offline Cyberdragon

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Re: Why are ICs/Semis black?
« Reply #9 on: May 03, 2021, 04:52:31 pm »
I think that the green marking of P-type semiconductors was some kind of Japanese standard? I have seen this green signature mostly or only with Japanese made components.

I believe the Soviets also had green semiconductors (in both metal and plastic).
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Online ataradov

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Re: Why are ICs/Semis black?
« Reply #10 on: May 03, 2021, 05:09:33 pm »
Soviet KT315/KT361 transistors came in orange, red, green, brown and other colors. I don't think color meant anything about the device itself, it may have coded the factory.

There is probably no specific reason why everything is black. It is just  easier to carry and characterize only one pigment.

A video from just today on that topic:

« Last Edit: May 03, 2021, 05:11:19 pm by ataradov »
Alex
 

Offline JohnnyMalaria

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Re: Why are ICs/Semis black?
« Reply #11 on: May 03, 2021, 05:27:17 pm »
1. Opacity
2. Quicker thermal equilibrium
3. Cheap. It's easy to maintain the color consistency when all you have is a single black pigment dispersed in a polymer matrix. Other colors would require multiple pigments and other additives which just adds to the complexity and cost of ensuring uniform encapsulation material.
 

Offline Benta

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Re: Why are ICs/Semis black?
« Reply #12 on: May 03, 2021, 06:27:48 pm »
Some opto-coupler devices are encapsulated in white plastic. Can anyone explain the reasoning behind that.

The original reason for that was to simplify the lead frame of the optocoupler (cost factor). The idea came from either Sharp or Toshiba, I believe.

A classic optocoupler has the LED and detector placed one above the other in a sort of Z/inverse-Z shape lead frame (seen from the side).
Using white epoxy, it's possible to place LED and detector side by side in a planar lead frame. The LED radiates vertically and the light is reflected to the detector by the white epoxy.
Much easier and cheaper.

Concerning other colours: many reasons for those. I remember repairing Salora TVs back in the 80s that had two fast SCRs (RCA types) in the horizontal output stage. They were identical, but paired, and one had to be a teeny weeny bit faster than the other for the circuit to work. One was green and the other was gray to ensure correct replacement.

 
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Offline magic

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Re: Why are ICs/Semis black?
« Reply #13 on: May 03, 2021, 07:00:29 pm »
No idea why black other than same reasons that applied to Ford T.

As for green, I have one such PNP made in commie Poland.
 

Offline retiredfeline

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Re: Why are ICs/Semis black?
« Reply #14 on: May 03, 2021, 10:53:38 pm »
Probably because it's cheapest, does the job, and people generally don't care about the look inside equipment. I have a few gray TTL chips from the 70s, a few red NPN and green PNP GE power transistors, and white optocouplers but the rest are boring black.
 

Offline james_s

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Re: Why are ICs/Semis black?
« Reply #15 on: May 03, 2021, 11:32:10 pm »
I've seen a lot of green transistors in Japanese electronics, which you don't see a lot of in general anymore.

I suspect like others have said, that black is the cheapest and the most opaque. If you want anything dark colored, it's probably easiest and cheapest to go with black, it provides a nice dark surface to print on and makes it relatively easy to get a consistent color between batches.

In thinking about this I'm reminded of the Dry-Z-Air devices that hold moisture absorbing salt crystals. They're black but at least the older ones if you look up close have blotches of all sorts of colors. I assumed they must empty all the remnants of plastic pellets from molding other goods and mix them all together to make those things as nobody really cares what color such a utilitarian device is.
 

Offline trophosphere

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Re: Why are ICs/Semis black?
« Reply #16 on: May 04, 2021, 03:20:43 am »
This is an interesting transparent DIP IC.
 
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Offline amyk

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Re: Why are ICs/Semis black?
« Reply #17 on: May 04, 2021, 03:43:12 am »
That one clearly has a sensor of some kind in the middle, which is why it's transparent. Optical mouses sensors are one type of IC currently in production with transparent packaging
 

Offline Canis Dirus Leidy

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Re: Why are ICs/Semis black?
« Reply #18 on: May 04, 2021, 03:16:32 pm »
I believe the Soviets also had green semiconductors (in both metal and plastic).
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Offline Caliaxy

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Re: Why are ICs/Semis black?
« Reply #19 on: May 04, 2021, 04:36:56 pm »
Maybe black plastic dissipates heat more efficiently?
 

Offline rdl

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Re: Why are ICs/Semis black?
« Reply #20 on: May 04, 2021, 06:52:30 pm »
I think it's mostly cost and light shielding. I know that when used to make paint carbon black pigments in general have the highest "hiding" power. White paint may need 20x as much or more TiO2 pigment (weight per unit volume) to achieve equivalent obliterating of the substrate.
 

Offline eti

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Re: Why are ICs/Semis black?
« Reply #21 on: May 04, 2021, 09:36:23 pm »
This is an interesting transparent DIP IC.

Gosh what a beautiful photo!
 

Offline rsjsouza

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Re: Why are ICs/Semis black?
« Reply #22 on: May 04, 2021, 11:01:37 pm »
I used to have a demo isolated DC-DC converter from Burr Brown on transparent silicon. It was very pretty, as it had a small toroidal transformer in the middle of its DIP16 packaging. Unfortunately I lost it.
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Offline BrianHG

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Re: Why are ICs/Semis black?
« Reply #23 on: May 05, 2021, 03:25:07 am »
Remember this thread: https://www.eevblog.com/forum/chat/why-are-most-semiconductor-cases-black/msg1632815/#msg1632815

IC / Transistor packages used to come in a rainbow of colors...
 
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Offline VK3DRB

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Re: Why are ICs/Semis black?
« Reply #24 on: May 09, 2021, 11:42:56 am »
Quite a few variants of opto-couplers are WHITE.

A better question is why are all power cords black. It would be much smarter to make them different colours so at least you have a better chance of knowing which one is plugged in where in the cable mess under your table.

 
 


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