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80 votes
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Why don't we make CPUs with 1000s of layers to make use of space in the third dimension?

The two killer reasons are yield, and heat. Yield. Every time you do a process step, you get less than 100% perfection. Let's say you get 99% perfection per step. In a process with 20 steps, you would ...
Neil_UK's user avatar
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42 votes
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Writable area on a PCB

Assuming white silk screen, just draw a solid box on the silkscreen layer. You can then write on it with a permanent marker. Here is an example from a board I made a while back: That was before I ...
Tom Carpenter's user avatar
37 votes

Why are most COB LEDs physically yellow?

The actual LEDs are probably blue and the encapsulation contains phosphors to generate the rest of the spectrum. The phosphors used will appear yellow. Figure 1. The blue peak is direct emission from ...
Transistor's user avatar
  • 177k
29 votes
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Why put unpopulated components on a BOM?

If you don't explicitly document that these components are not to be placed, you will inevitably have your manufacturing team notice that there is a location on the board with no corresponding line in ...
The Photon's user avatar
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24 votes
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What is this small unconnected solder blob on this PCB?

It's most likely a type of fiducial marker, used by a pick-and-place machine to correctly place the SMD parts on the copper side of the board.
Dave Tweed's user avatar
  • 174k
24 votes

Why do manufacturers label differently seemingly identical components?

The way the electronics industry is supposed to work (but rarely does): When you buy a component from a supposedly reputable component vendor like Arrow, Avnet etc, they are supposed to keep tabs on ...
Lundin's user avatar
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23 votes
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Why do manufacturers label differently seemingly identical components?

So there's differences. Thankfully, they decided not to use the same name for different things, that would be much more confusing than using different names for similar things. Strategic benefit is ...
Marcus Müller's user avatar
22 votes
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What are some reasons for hand painted dots on chips?

These are put there during assembly and test of the PCB and can mean anything the manufacturer wants to mark. Often such a dot is put on a microcontroller, when the firmware is successfully programmed ...
jusaca's user avatar
  • 9,609
21 votes

Do manufacturers try make their components as close to ideal ones as possible?

Yes - but to a budget. For example, in the case of resistors, there are various tolerances available which tell you how much the actual ohm value may differ from the stated value. 5% tolerance used ...
pjc50's user avatar
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21 votes
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Which is better - components on both sides or components on one side of the PCB?

PCB size is not the only cost consideration and you need to consider recurring costs vs. one time (non-recurring) costs (some of the non-recurring may actually occur more than once for a 50k run). ...
Peter Smith's user avatar
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20 votes
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Mounting components on both sides of a PCB

First off, use a 4 layer board. Not only does it make layout easier but inner ground and power planes provides a barrier against front/back crosstalk. Also, 4 layer is not much more expensive than 2 ...
Dirk Bruere's user avatar
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20 votes

Who is the main manufacturer of jelly bean parts?

There are some industry standards, and a lot of de-facto standards, and more ad-hoc imitation. Back in the day, JEDEC registered parts could be produced by anyone, and sold as that part number so long ...
Tim Williams's user avatar
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19 votes

Why don't we make CPUs with 1000s of layers to make use of space in the third dimension?

Heat removal is the issue. Already some chips have higher energy density than a nuclear reactor. Consider a hair_drier ---- 1,500 watts with a air_blast fan to cool the tungsten coils. And the coils ...
analogsystemsrf's user avatar
19 votes
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Why are most COB LEDs physically yellow?

Because white LEDs do not actually exist. The yellow you are seeing is a phosphor (a substance that absorbs light of one color and emits it again in another color) known as cerium-doped yttrium-...
forest's user avatar
  • 538
18 votes

Writable area on a PCB

A common practice is to leave a square area on your PCB, filled with white silkscreen as a background. If you would like to write on the PCB with something other than a permanent felt marker (e.g. a ...
Daniel's user avatar
  • 1,620
17 votes
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What is a "risk wafer"?

When you release a design to manufacturing, i.e. Tape-out, fracture (mask making) and then lot start what is normal is that you start a ES (engineering sample) lot that is smaller than a full ...
placeholder's user avatar
  • 30.2k
17 votes

Mounting components on both sides of a PCB

Adding to Dirk's Answer Be aware, mounting on both sides of a board may not buy you as much real estate as you might be imagining. When it comes to board density, your ability to route traces tends ...
Trevor_G's user avatar
  • 46.8k
16 votes

Environmentally sustainable electronics

Reliability? There is an entire field of expertise on building robust electronics. This requires vigorous testing, and thorough design. This will be more expensive and increase time-to-market. But ...
Arcatus's user avatar
  • 1,845
16 votes

Component Tolerance Probability

The problem is, nobody knows. Each manufacturer may work differently. You might ask a specific manufacturer about a specific series of resistors how they are binned, but why would they reveal that ...
Justme's user avatar
  • 155k
15 votes

Is it practical for firmware to be uniquely identified in production

You may be asking about a software-only solution but if you are able to add a cheap IC to your board, you can use a 'Silicon Serial Number' chip. These are tiny ROM chips that each device contains a ...
TonyM's user avatar
  • 23.3k
15 votes
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Is it practical for firmware to be uniquely identified in production

Most production programmers are capable of inserting a unique serial number into the programmed memory, its a process normally called serialization. This is a grab of the Serialization screen from an ...
Steve G's user avatar
  • 5,315
15 votes
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'Pick and place' feature in connectors

The Pick-and-Place version of the connector will have a piece of tape (probably something like kapton) over the open top end of the connector, or some other firm flat surface, so that a vacuum pick-...
brhans's user avatar
  • 14.7k
14 votes

Writable area on a PCB

Yes. You can write on basically any part of a PCB with a permanent marker. If you want, you can also use your silkscreen layer to provide e.g. a white background, or checkmark boxes etc. This is ...
Marcus Müller's user avatar
13 votes

How much does it cost to have a custom ASIC made?

Now by end of 2018, a company is working on a platform "Itsy-Chipsy" (assuming a software tools collection plus fab services) to produce two prototype chips for about $400 at a 350x350um size which ...
minghua's user avatar
  • 555
13 votes
Accepted

Anyone know the premise of this PCB assembly note?

It's clearly to get rid of moisture, probably to keep the steam from pushing BGAs or CSP packages off the board (maybe from moisture trapped in tented vias, microvias or other places), but I didn't ...
Spehro Pefhany's user avatar
13 votes

What exactly makes small quantity PCB production costly compared to large quantity PCB production?

Firstly the manufacturer needs to check your uploaded board for any irregularities. This is done by hand by engineers, so will cost a fair bit. If it is checked, the manufacturer needs to send your ...
Ananas_hoi's user avatar
13 votes

Question on "Parts should be used within 5 days after opening." statement on component shipping package

It's to do with Moisture sensitivity. When the components were packaged, there were done so in a controlled environment, particularly with regard to humidity (or lack thereof, you can see that bag was ...
LordTeddy's user avatar
  • 2,372

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