Reliability problems on NHD-0420CW-AB3

ademarco

• January 13, 2020 03:47

Hello,

we designed an electronic board with the NHD-0420CW-AB3 display and we have some faulty devices.

As shown in the attached picture, the pixels that makes each character are not fully clear with the same brightness.
The display is driven through I2C and pin 2 and pin 3 of the display interface are at +5VDC.
What could be the reason of the failure?
The failures emerged after only one month @ 25 deg C constant temperature.

Thanks, regards.
Alberto

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  Alee_S

  • January 22, 2020 15:42

  Hello ademarco,
  
  Unfortunately our NHD-0420CW-AB3 display does not support I2C interface at 5V conditions, which could be why you are experiencing issues even at normal operating temperatures. We have known of this issue on Slim Character OLEDs which affects its operation when used in I2C mode at 5V conditions, and have reflected this appropriately in our datasheets.
  
  I2C interface has been tested, verified, and can be safely operated at 3.3V or low operating voltage conditions, and both parallel & serial interface conditions are supported at both low operating voltage and 5V conditions.
  
  Best,

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  ademarco

  • January 31, 2020 06:51

  Hello Alee,
  
  thanks for your reply.
  It has been open another post by Terry with the title "NHD-0220CW-AB3 Pixel Problem".
  In his case, even if the display has been powered at the right 3.3 VDC voltage, he gets the same problem that I have on the pixel intensity.
  Are you sure that in my case the problem is only due to a wrong supply voltage?
  I had the problem after 1 month at room temperature, he had a problem after less than one year, in any case we are very far from the claimed MTBF value.
  Can you suggest some further check in order to find out the real cause of the problem?

  
  Please keep me posted.
  Thanks in advance.

  
  Best regards.
  Alberto

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  Alee_S

  • February 10, 2020 16:58

  Hi Ademarco,
  Thanks for sharing your update.
  
  Since it works at a 3.3V supply, it is like the supply voltage is not at fault here. However is it possible these displays are being used in a high-humidity environment? This may cause some pixel fading over a certain time period of the displays use.
  
  Best,

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  ademarco

  • February 11, 2020 01:11

  Hello Alee_S,
  
  in my case the displays are not in a high-humidity environment.
  I have now to design a new display electronic board and I don't know if go on to use the New Haven display again.
  This kind of failure is not acceptable, specially for our final customer.
  Please let me know if there is something else to check in order to discover the real cause.
  Thanks and best regards.
  
  Alberto

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  Alee_S

  • February 24, 2020 14:26

  Hi Ademarco,
  
  It is also possible this could be an indication of ESD damage, considering the failure occured during normal operating conditions and happened over a short period of time.
  
  Best,

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  sandrom

  • March 04, 2020 12:42

  Let me reply to this issue.
  In a previous post it is stated that the reason of the problems with 5V power supply on the display NHD-0420CW-AB3 is the instability of the I2C interface.
  
  I don't understand how it could be related to the oled reliability and in the pixel degradation.
  
  Can you explain please?
  
  Thanks
  Sandro

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  Dannierig

  • March 12, 2020 09:40

  So this simply can't cause pixel degradation, Sandro?

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  sandrom

  • March 14, 2020 02:41

  can you explain?

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  Ted M.

  NHD Staff

  • March 16, 2020 15:49

  Hi Sandrom,
  
  Does the pixel degradation occur only on pixels that are always lit?
  To prevent uneven pixel wear on a passive matrix OLED display, it is recommended to blank the screen often or when not in use.
  Another method would be to scroll the characters across the display randomly in order to allow for even pixel wear.
  
  Regards,

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  sandrom

  • March 17, 2020 08:54

  Hello,
  Yes our problem is the degradation occurs only on pixels that are in use.
  We will study software modifications following your suggestions.
  I have another question:
  Can direct sunlight affect or accellerate the degradation process?
  
  Thanks.
  Sandro

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  Ted M.

  NHD Staff

  • March 17, 2020 11:18

  Hi Sandrom,
  
  Prolonged direct sunlight on the OLED screen may produce an excessive amount of heat as well as damaging UV exposure. 
  Both of these conditions will accelerate pixel fading and create early failures in the OLED material.
  
  Regards,

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