Why are ICs/Semis black? - Page 1
Forum section: electronics / general

author: PStevenson
author_rank: Regular Contributor
timestamp: May 03, 2021, 11:34:59 am
content: 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?

author: Brumby
author_rank: Unknown
timestamp: May 03, 2021, 12:10:18 pm
content: 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.

author: newbrain
author_rank: Super Contributor
timestamp: May 03, 2021, 12:20:55 pm
content: Quote from: Brumby on May 03, 2021, 12:10:18 pmWhen 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 timean 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 picturesSome 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.

author: G7PSK
author_rank: Super Contributor
timestamp: May 03, 2021, 12:51:08 pm
content: 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.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 03, 2021, 12:51:59 pm
content: Quote from: newbrain on May 03, 2021, 12:20:55 pmOr more recently, a design flaw with the Raspberry Pi 2:

author: srb1954
author_rank: Super Contributor
timestamp: May 03, 2021, 01:13:14 pm
content: Quote from: Brumby on May 03, 2021, 12:10:18 pmSome opto-coupler devices are encapsulated in white plastic. Can anyone explain the reasoning behind that.

author: beanflying
author_rank: Super Contributor
timestamp: May 03, 2021, 01:36:12 pm
content: Quote from: srb1954 on May 03, 2021, 01:13:14 pmVery 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 03, 2021, 01:53:22 pm
content: 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.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.Tim

author: Yansi
author_rank: Super Contributor
timestamp: May 03, 2021, 01:59:57 pm
content: 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.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 03, 2021, 04:52:31 pm
content: Quote from: Yansi on May 03, 2021, 01:59:57 pmI believe the Soviets also had green semiconductors (in both metal and plastic).

author: ataradov
author_rank: Super Contributor
timestamp: May 03, 2021, 05:09:33 pm
content: 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:

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 03, 2021, 05:27:17 pm
content: 1. Opacity2. Quicker thermal equilibrium3. 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.

author: Benta
author_rank: Super Contributor
timestamp: May 03, 2021, 06:27:48 pm
content: Quote from: srb1954 on May 03, 2021, 01:13:14 pmThe 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.

author: magic
author_rank: Super Contributor
timestamp: May 03, 2021, 07:00:29 pm
content: 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.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: May 03, 2021, 10:53:38 pm
content: 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.

author: james_s
author_rank: Super Contributor
timestamp: May 03, 2021, 11:32:10 pm
content: 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.

author: trophosphere
author_rank: Frequent Contributor
timestamp: May 04, 2021, 03:20:43 am
content: This is an interesting transparent DIP IC.

author: amyk
author_rank: Super Contributor
timestamp: May 04, 2021, 03:43:12 am
content: 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

author: Canis Dirus Leidy
author_rank: Regular Contributor
timestamp: May 04, 2021, 03:16:32 pm
content: Quote from: Cyberdragon on May 03, 2021, 04:52:31 pmWell, it mostly depended on what kind of filling was put in the cookies:http://www.155la3.ru/k405.htmhttp://www.155la3.ru/k828.htm

author: Caliaxy
author_rank: Frequent Contributor
timestamp: May 04, 2021, 04:36:56 pm
content: Maybe black plastic dissipates heat more efficiently?

author: rdl
author_rank: Super Contributor
timestamp: May 04, 2021, 06:52:30 pm
content: 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.

author: eti
author_rank: Super Contributor
timestamp: May 04, 2021, 09:36:23 pm
content: Quote from: trophosphere on May 04, 2021, 03:20:43 amGosh what a beautiful photo!

author: rsjsouza
author_rank: Super Contributor
timestamp: May 04, 2021, 11:01:37 pm
content: 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.

author: BrianHG
author_rank: Super Contributor
timestamp: May 05, 2021, 03:25:07 am
content: Remember this thread:https://www.eevblog.com/forum/chat/why-are-most-semiconductor-cases-black/msg1632815/#msg1632815IC / Transistor packages used to come in a rainbow of colors...

author: VK3DRB
author_rank: Super Contributor
timestamp: May 09, 2021, 11:42:56 am
content: 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.

author: GlennSprigg
author_rank: Super Contributor
timestamp: May 09, 2021, 12:20:20 pm
content: This may be 'slightly' off topic, (but people that know me... well... you know...)...Back in the 60's early 70's, when I first started playing with 'electronics', we often had BLACK painted Glass-Enveloped Transistors,which from memory were in the 'OCxx' series... Years later, I had a 'Debate' online with an old guy that had actually BUILT them !!Now I told him how we would scratch the black paint off, to make them Light-Sensitive Transistors!!! Was true, but he didn't believe it.Also around that time (and earlier!), certain old valves/tubes had their glass body spray-painted black, and sometimes gold... Althoughfor different reasons! although SOME clear-glass tubes actually had an external light-source close to them, in order to 'excite' the coatedplates, that's beyond the discussion here!!...Anyway, their main reason for 'coating' in the above paragraph, was to HIDE what the manufacturers had done technology wise, inside.But NOT to stop giving away 'good' secrets, but out of embarrassment when technology had 'improved', and a cheap manufacturer wasnot using the latest science in their Plates/Coatings & 'Getter' technology, that was obvious without the Paint!

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2021, 04:42:39 am
content: Quote from: GlennSprigg on May 09, 2021, 12:20:20 pmI thought it was a conductive coating for shielding purposes? I don't see much value in trying to hide what's inside, the average person would never know the difference and anyone who actually wanted to see what was inside could just break it open.There were also some tubes that had metal envelopes, not a metal shell over a glass envelope but the metal was actually the envelope.

author: Gyro
author_rank: Super Contributor
timestamp: May 10, 2021, 09:42:46 am
content: Quote from: GlennSprigg on May 09, 2021, 12:20:20 pmHe may not have believed it, but Mullard certainly did!The original OC71 had clear protective grease around the junction. People (we) would scrape the paint off and use them as phototransistors. Mullard got wind of this and started using an opaque white grease in them. They then sold the OCP71 phototransistor (clear grease) for a very significant markup! Irrc, it had a little plastic sleeve around the bottom with the part number on.I even heard of people mounting the white grease transistors in spin dryers to centrifuge the grease down to the bottom of the package. Others would carefully file a groove around the bottom of the package, crack the glass top off and dissolve the grease away (I tried that one). Electronics magazines of the time (Practical Electronics) were full of similar reader suggestions.

author: Gyro
author_rank: Super Contributor
timestamp: May 10, 2021, 10:01:57 am
content: Quote from: james_s on May 10, 2021, 04:42:39 amYes, it was usually for screening - they had to leave a clear circle around the anode / grid top cap. You'd find it on RF tubes rather than LF output ones.

author: David Hess
author_rank: Super Contributor
timestamp: May 11, 2021, 03:28:29 am
content: Quote from: T3sl4co1l on May 03, 2021, 01:53:22 pmSome optocouplers include an electrostatic shield between the elements to reduce coupling capacitance. I wonder if it is a metal screen or tin oxide film.QuoteI have seen plastic packaged thyristors and very rarely power transistors in various shades of red.Quote from: GlennSprigg on May 09, 2021, 12:20:20 pmAn early design that I did had to use glass diodes for input protection which also made it photosensitive. So we ended up painting the glass diodes after assembly.Old glass diodes were sometimes painted black.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: May 11, 2021, 07:00:44 am
content: Quote from: Gyro on May 10, 2021, 09:42:46 amI once made remote xenon flash synchronisers using scraped (and scrapped, probably due to leakage) OC71 transistors triggering a SCR. Worked great.

author: GlennSprigg
author_rank: Super Contributor
timestamp: May 14, 2021, 11:58:40 am
content: Quote from: james_s on May 10, 2021, 04:42:39 amHiJames. Sorry about the delay! Yes, there were various reasons for outer coatings... And there were (a lot!) with metal casings, (as you say, notthe clipped-on outer-shell for 'shielding'), and those were 'mainly' used in Military grade equipment, and mainly due to their physical robustness !However, some coatings were to 'mask' what's going on inside at the time! I was 1st commenting just from memory, but I've found this now, thatmay give further evidence... Below is one example from 'Wikipedia' talking about the 'Mullard/Philips' partnership...https://en.wikipedia.org/wiki/MullardNot far from the top, on the right-hand side, you will find this photo, and underneath it a 'Description'...A Mullard TDD4 valve. The gold spray coating served no purpose other than to hide the blackened interior,as Mullard valves were still manufactured using the azide process, long abandoned by other makers.

author: james_s
author_rank: Super Contributor
timestamp: May 16, 2021, 12:57:40 am
content: But is that to hide it from prying eyes, or just dress it up and make it look fancy? They mention the blackened interior which makes me suspect they're referring to a getter flash which was black. It may be they wanted to avoid people thinking the tube was burned out or something due to a darkening resembling a well used light bulb.

author: Canis Dirus Leidy
author_rank: Regular Contributor
timestamp: May 16, 2021, 06:15:33 pm
content: More on the question of package colors.The old 237-series ICs with a "Kulon" case. Mostly dirty-white, but there are also colored plastic.