Looking for legacy IC manufacture date codes for M27C EPROMs

[BobFromAccounting]

Hello all.  Tasked to replace an old 128Kx8 EPROM, but the folks paying the bills want me to decode the ICs manufacture date code for QA reasons.  Does anyone know of any URLs?  The ST first data book I found was created long before this IC existed.  The key details are below:

 

Below quartz window of die with 2 banks x 1  

Row 1: ST logo B88HA
Row 2:9231E5S

Row 3:M27C1001

Row 4:        -20F1

My best guess is the 128Kx8 (confirmed by reading manufacture code on the programmer and prior EPROM knowledge and abuse) STMicro EPROM 200 ns with 0 to 70 C temperature range. Guessed at date of 1992 week 31.  No idea about where it was made or what the E5S means or what the B88HA translates to in locations.

Also I have another EPROM with

Below quartz window of die with 4 banks 2x2 matrix

ST logo B88GA
9227
MC27C1001

          -20F1

Just want to be sure I can explain the die differences if anyone asks about counterfeits.  I assume the differences are due to a process change and the wafer dies delivered to different packaging plants.

 

Thank you in advance. 

[Peter BENSCH]

Welcome @BobFromAccounting, to the community!

Phew... those are really very... veeeery old devices, which were discontinued decades ago, which is why there is no more information available about them from STMicroelectronics. Most of the people who worked on them back then are already retired.

Perhaps something can be found in the depths of the otherwise never-forgetting internet, otherwise it is extremely unlikely that anyone will be able to comment on this.

 

Perhaps we can guess something from the structure if you insert photos of the devices that are as legible as possible. However, it looks like the first of your devices is from 1992, cw 31 (9231) and the second from 1992, cw 27 (9227), but I could be wrong. For newer devices, the date code consists of YWW, i.e. the last digit of the year and two digits cw.

Hope that helps? 

Regards
/Peter

Hi Bob,

For older ST EPROMs like the M27C1001, official public documentation on detailed date-code decoding (especially internal codes like B88HA or E5S) is unfortunately very limited. Your interpretation of 9231 as 1992, week 31 is consistent with how STMicroelectronics and other vendors marked devices during that period. Variations in die layout (2-bank vs 4-bank) are commonly explained by process shrinks or second-source wafer fabs, rather than counterfeits.

In similar legacy-component investigations, I’ve found that legacy IC identification resources can be useful for cross-checking markings, die revisions, and historical packaging practices when official datasheets fall short.

Unless there are electrical anomalies, your assumption about process changes and different assembly sites is reasonable and defensible for QA documentation.