Holes in optical sensor IC, why so many?

Discussion in 'General Electronics Chat' started by eblc1388, Oct 24, 2010.

  1. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    I have noticed there are many holes on the surface of the optical sensor IC used in optical mouse.

    They are normally covered by a piece of black plastic inside the mouse body.

    So they are not likely to place a part in sensing the reflected light from the surface the mouse moves on.

    So why are they there?

    [​IMG]
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It is unclear (also from the datasheet) why there are so many holes in the chip.
    I have attached the datasheet to look at.

    Bertus
     
  3. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    I was thinking the holes might be there to make the IC body less rigid as the IC is made up of two parts that snaps together.

    Or they are there to aid alignment as several vertical steel pins are inserted into the holes of the top and matching holes in bottom parts when pressure is applied to snap the two parts together.

    The holes are not placed in a regular pattern as shown in the follow image of another optical sensor.

    [​IMG]
     
  4. tom66

    Senior Member

    May 9, 2009
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    Perhaps they are for cooling. I think the sensors are heat sensitive as well.
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Cooling? Why cover with tape then?

    I like the mechanical suggestion, but then why so many? And why have different arrangements for different chips? Do they dead end into plastic or is there something beneath them?

    Perhaps they allow access for testing, electronic alignment and programming after manufacture. That would explain why the arrangements vary with different devices and why they are subsequently covered. How about probing them on a waste chip with an ohmmeter?

    John
     
  6. Markd77

    Senior Member

    Sep 7, 2009
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    I've had a look at an A2030 sensor which has 16 pins. There are 17 small round holes plus the big circular dent. Looks like metal at the bottom of the holes.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    I share the impression that the holes serve as access points for testing or aligning the optical sensor during the manufacturing process.

    hgmjr
     
  8. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    This might be it.

    Also for some strange reasons the pins are normal 0.1" spacing like most plastic DIP ICs but offset by 0.05" between the two opposite rows.

    It will not fit onto an usual hobby circuit board with 0.1" pitch pads.
     
  9. Markd77

    Senior Member

    Sep 7, 2009
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    For breadboarding, you could use 2 breadboards pushed together with the chip over the gap. Only works on breadboards without power rails above and below.
     
  10. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    My guess goes the mechanical route, maybe to support the optics during the encapsulation process.
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    That's easy, the right-hand side was designed after the lunch break. It was the usual 3 Martini lunch.

    John
     
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