Solutions to prevent X-ray damage to Flash Memory
Author：KANA

Program overview

At present, due to the rising storage density of Flash Memory storage devices and the continuous updating of chip production process nodes, the process within 20 nm is becoming more and more common in the manufacturing of memory devices. The continuous expansion of line width not only brings challenges to manufacturing, but also brings new challenges to the X-ray inspection during the assembly process. The experiment proves that the memory chip will lose the data due to the electronic transition under the X-ray irradiation for a long time, so that the product system will fail. X-ray inspection is an indispensable reliability means in the assembly process, in order to avoid damage to the chip, we propose the following solutions for your reference to help factory engineers in the use of X-ray equipment reasonably avoid product failure.

1. X-ray absorption ability test of Flash memory

1. Test process:

• KV=100KV, focus to chip distance =200mm
• Set different target powers to record the X-ray intensity without the chip placed
• Set different target powers and record the X-ray intensity after placing the chip
• Calculate the X-ray intensity difference, which is the X-ray energy absorbed by the chip

2. Test results:

Note: Due to range limitation, RADEYE G-10 (max100mSv/h), the value in red is the calculated value

Flash memory 吸收X射线能力测试X-ray absorption capability test of Flash memory

Conclusion:

KV=100KV, FOD=200mm
X-ray (mSv/h) energy absorbed by the chip = 18+ 22 * (Target Power - 0.2W)

3. Define the maximum allowable detection time based on daily detection parameters

Select the usual detection setting condition:
• KV:100KV
• Target power 0.5W
• Sample to focus distance (FOD): 27.5mm

根据三星芯片规格:最大容忍X光的吸收量 0.5Ra，按照70%的安全阀值选择 3.75mSv 为安全值，确保经过X-ray 检查后，芯片正常工作可以算出最大检查的时间。According to Samsung chip specifications: the maximum tolerance of X-ray absorption is 0.5Ra, and 3.75mSv is selected as the safety value according to 70% of the safety valve value to ensure that the maximum inspection time can be calculated after X-ray inspection.
Detection time (s) = 3.75/449.59 * 3600 = 30 Sec
The maximum X-ray irradiation time of the sample is less than 30 sec. The X-ray energy absorbed by the sample is less than 0.375Rad, and the inspection process is safe.

4. Problem: In the actual sound field process, it is difficult to control the X-ray inspection time within 30 seconds, in addition, to achieve standardized batch operation, it is also different from the usual operation.

Second, how to prevent the damage of the memory chip during the X-ray inspection

1. Add a collimator

Reduce the XX ray cone Angle from 170 degrees to about 40 degrees.
Purpose: To detect one of the chips, the other chips will not be illuminated (memory chips are usually clustered).
As shown below

Fixed detection parameters using FNC:
KV: 100KV
Target power :0.5W
Distance between focus and sample :27.5mm
The detection is fully automatic and the total exposure time of the chip is controlled by the machine

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