31
votes
Accepted
Why are resistors tolerances relative instead of absolute?
I'll try to simplify this for you... Hopefully successfully.
If you imagine making a resistor just by cutting pieces of a material, let's say a special metallic film;
You want your resistor to fit ...
- 18.4k
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 ...
- 1,845
15
votes
Accepted
What shapes can IC dies be?
The main restriction is that the easiest and cheapest way to cut a wafer is in straight lines that go all the way across the wafer. It's hard to start and stop cutting in the middle of the wafer, ...
- 35.2k
14
votes
How do components not get knocked off or fall off during reflow?
Dots of glue are used where components may fall off. If components are on the bottom side of the board, then all are glued. Boards with bottom side components must be raised on stand-offs to provide ...
- 17k
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 ...
- 407k
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 ...
- 594
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 ...
- 2,372
12
votes
Accepted
How do components not get knocked off or fall off during reflow?
CNC-machined carriers (pallets nb thanks to Aaron for the term) are generally used. The panel or board goes in the carrier and the carrier goes on the conveyor belt. They're made from a black high ...
- 407k
10
votes
Accepted
Solution to detect bad vias in production process
There are a number of reasons for cracked vias and virtually all of them are caused, to a greater or lesser degree, by CTE issues.
Looking at this datasheet (a very commonly used material in the ...
- 22.5k
10
votes
Accepted
Question on "Parts should be used within 5 days after opening." statement on component shipping package
The parts can survive well beyond 5 days. However, the component is moisture sensitive. And if you don't store it well (in a well-controlled environment), it could cause SMT assembly issues such as ...
- 8,361
9
votes
How do components not get knocked off or fall off during reflow?
Our assembly house uses two different solders. First, they use a solder with a higher melt temperature, and solder the components on the top side. They flip the board, then use a solder with a lower ...
- 1,329
8
votes
What exactly makes small quantity PCB production costly compared to large quantity PCB production?
Your questions is somewhat vague. What is "small number"? What is "large number"? Making onesies is always going to be expensive, but when using PCB batching services at least you'...
- 5,469
8
votes
Environmentally sustainable electronics
Here are a few more points. I approach this as a former systems engineer, so these deliberately look at the big picture rather than details of electronic component selection etc., but this needs a ...
- 2,803
8
votes
What shapes can IC dies be?
Occasionally you see some unusual shapes, especially when the target structure is circular:
https://www.photonics.com/Buyers_Guide/ProdSpec/Sensors_Detectors/Photodiode_-_AXUV20A/psp7337
Aside from ...
- 17.6k
7
votes
PCB design rules
Almost every PCB vendor will have their capabilities listed on their website.
For example:
http://www.4pcb.com/pcb-capabilities.html
https://www.protoexpress.com/content/capability.jsp
http://www....
- 1,967
7
votes
Environmentally sustainable electronics
I think you should make it win-win, both for your company and the customer. Some ideas:
Lower power use
This is marketable, and translates directly into cost savings for the customer. Especially if ...
- 79.5k
7
votes
What shapes can IC dies be?
While the questions asks What other tesselations can they be cut into?, a counter argument is what are the reasons why rectangular shapes are used.
From searching found other answers which gives the ...
- 5,293
6
votes
Accepted
Why do some exposed pads have small tabs, and does my PCB footprint need them?
I can't speak for all manufacturers, but sometimes thermal pad is the bottom of the die carrier, as that ensures thermal performance. Die carriers could be fed from a reel, that has stamped die ...
- 3,604
6
votes
Why are the challenges in using SRAM over DRAM for main memory?
The simple answer is that SRAM requires more transistors to implement one bit of memory.
Several designs exist, and they tend to use four or more MOSFETs per bit.
DRAM on the other hand, only requires ...
- 320
6
votes
Accepted
Why are the challenges in using SRAM over DRAM for main memory?
Has any today's major advances in semiconductor manufacturing,carried over to SRAM technology to mitigate some of its issues?
No they have not, and in fact SRAM density has not scaled down with ...
- 17.6k
5
votes
Why are resistors tolerances relative instead of absolute?
This is more of a materials science or manufacturing question. It really depends on the resistor technology also the process used for manufacturing.
Source: Chip Resistors Information
The ...
- 84.8k
5
votes
How do components not get knocked off or fall off during reflow?
First, the boards don’t sit directly on the conveyor belt. They are in carriers, and so their surfaces make no direct contact with the belt or anything else.
Now, what holds the backside components in ...
- 55k
5
votes
Accepted
Why do JFET use buried channels?
A Premise. The physical realization of the device must follow as closely as possible the structure identified by mathematical model behind it. Otherwise, second order effects which are considered to ...
- 3,385
4
votes
Anyone know the premise of this PCB assembly note?
Usually baking for long periods of time like that is to eliminate moisture in the product. If there is moisture inside the PCB, the quick ramp up to ~250 C during the reflow process can cause this ...
4
votes
Why can my bare PCB be magnetized?
ENIG plating translates to "Electroless nickel immersion gold" (for neophytes).
This means gold plated copper surfaces using nickel as intermediary layer between copper and gold.
Then, if your PCB ...
4
votes
Solution to detect bad vias in production process
I can't post comments due to my low reputation, but I thought the idea may still be worth sharing.
As others pointed out, cracks can reveal themselves when the board is thermal cycled. Inspecting the ...
- 303
4
votes
Accepted
Can through-hole leads be cut level with the PCB back while maintaining good connectivity?
IPC Class 1 and 2 require only that the "End is discernable in solder".
Cutting the leads before soldering would likely expose some non-plated material which might affect the joint (...
- 407k
4
votes
What does it mean when it is said that an Intel CPU is assembled in Country X?
Usually "assembled" means that some action was performed that changed the state of product, for example by combining different components, perhaps from different suppliers.
However there was ...
- 407k
4
votes
Behaviour of uninitialised RAM in an ASIC
Big picture, you cannot count on any 'non-volatile' behavior from an ordinary SRAM. You must initialize it when your system starts up, or within your driver program for a peripheral. There is no such ...
- 55k
Only top scored, non community-wiki answers of a minimum length are eligible