Author Topic: why most computer chips have black cricle on package??  (Read 1094 times)

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Offline aqarwaen

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why most computer chips have black cricle on package??
« on: February 19, 2018, 04:06:07 pm »
simple question why most computer chips have black cricle on package??i noticed that most have slightly different color cricle on chip packaxe..does it have any specific use?
 

Offline Ice-Tea

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Re: why most computer chips have black cricle on package??
« Reply #1 on: February 19, 2018, 04:08:42 pm »
Might help if you had picture showing is what your question is about... But perhaps you are referring to the dot that denotes pin 1?

Offline @rt

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Re: why most computer chips have black cricle on package??
« Reply #2 on: February 19, 2018, 04:11:41 pm »
I’ll bet. OP meant PicAxe. a Pic micro.
 

Offline daqq

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Re: why most computer chips have black cricle on package??
« Reply #3 on: February 19, 2018, 05:01:00 pm »
Generally they indicate the position of pin 1.
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Offline ajb

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Re: why most computer chips have black cricle on package??
« Reply #4 on: February 19, 2018, 06:28:57 pm »
There are pin 1 marks, and there area also molding marks (either injection points or ejector pin marks, I guess).  The latter are usually on the bottom, but you'll occasionally see them on the top as well--and if you're very unlucky, sometimes the molding mark on the top is much more obvious than the pin 1 mark, and you will have to make sure your assembler does not get confused.
 
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Offline Brumby

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Re: why most computer chips have black cricle on package??
« Reply #5 on: February 20, 2018, 12:40:06 am »
Might help if you had picture showing is what your question is about...

I must agree.

The question makes reference to colour, but other than that, gives no indication of their nature (whether molded or printed), their size (is it a dot more than a circle?) or location (in a corner, on a side, in the middle somewhere).

Any other comments about pin 1 identification are just guesses and unless we can be sure of what you are asking, they could be completely misleading.  For starters, I am not aware of any pin 1 identification that involves colour.

Picture, please.

I know it could be a challenge to photograph something so small - but use good lighting and get as close as you can and still get a sharp image.
 

Offline @rt

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Re: why most computer chips have black cricle on package??
« Reply #6 on: February 20, 2018, 06:00:19 am »
A picaxe is a Microchip pic. It’s pin 1.
 

Offline T3sl4co1l

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Re: why most computer chips have black cricle on package??
« Reply #7 on: February 20, 2018, 09:04:31 am »
https://www.google.com/search?q=ejector+pin+marks

Probably those.  I don't know if pin-1 markings are formed in the mold as a normal feature, or an ejector pin mark (it's possible).  Possibly, the marks seen on the bottom side of the package are ejectors, if present (and if not obviously a mold mark).

Semiconductor packages aren't exactly injection molded.  Actually I've not seen exactly how they do it.  A mold is definitely involved, and some means of injecting the resin will be needed, and probably some means of removing the part once finished.  The main difference, I would think, is that the mold doesn't necessarily have to be cooled after injecting and setting the resin (which is likely heat activated; whereas injection molded thermoplastics must be injected hot, then the mold quickly cooled, to harden the part enough to push it out).  Since most components are leaded (including QFN and LGA parts, before final shaping, I think?), or flanged (many LGAs and BGAs have a molded plastic cover over the chip, sitting on top of the slightly larger interposer, a fine pitch PCB, which would also serve as a flange and could be oversize for handling before final shaping), ejector pins might not be needed over the component body area.

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