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PCB Tech
MSL certification and upgrade of PCB circuit boards
PCB Tech
MSL certification and upgrade of PCB circuit boards

MSL certification and upgrade of PCB circuit boards

2021-10-24
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Author:Downs

1. The certification and upgrade of moisture sensitive water-based MSL

(1) Certification MSL

The process of obtaining moisture sensitive water (MSL) for PCB circuit boards. All new products that have not been certified must start with the lowest level (Level 6) in Table-1, that is, after passing the Level 6 exam, they can be upgraded to Level 5a, and then upgraded to Level 5, etc. . This kind of upgrades up until the level cannot be cleared, that is, the level 1 it belongs to is declared.

(2) Upgrade MSL

Anyone who has been certified to a Level 1 seal and wants to upgrade again must pass the "additional reliability test" first. This test requires two batches of 22 samples in total, and the two batches must be drawn from two or more discontinuous production batches. The appearance of each batch of products should be the same as possible, and each production batch must pass all the manufacturing processes in advance.

The 11 samples taken in each batch also need to complete all the manufacturing processes. For samples that enter the upgrade test, they must continue to perform the moisture absorption test listed in Table 5-1 until the subsequent electrical and visual inspections are passed. The supplier must first perform the self-certification affirmation level before sending it to the customer for further level certification.

pcb board

(3) Moisture absorption technique

The contents of Table 5-1 first perform a placement test on the "hygroscopic conditions" of a certain water and Huai table, and then perform various electrical tests and visual inspections, and complete the "Ultrasonic Scanning Microscope" (C-SAM) inspection Bottom line. However, the purpose of this specification is not for the "layering" of the initial inspection, but to determine the "Huai Rules" for acceptance or rejection.

The seals to be tested must be baked in an oven at 125°C for 24 hours to remove moisture, so that the moisture absorption test can be carried out in a dry condition. However, when the second highest and highest water level test is performed, the required baking and dehumidification can still be determined according to the actual situation and other conditions before the implementation of the "Double Eighth Five-Year" moisture absorption 168 hours (7 days).

2. Moisture absorption in the front section and reflow in the back section

(1) Moisture absorption test

Place the semiconductor packages to be tested for moisture absorption in a clean and dry tray. They must not touch or overlap each other. They must comply with the JESD625 regulations throughout the process, and avoid "static damage". The content of the following Table 5-1 is the semiconductor package components, which can be divided into eight types of moisture sensitive water (MSL). After opening the package and before completing the assembly and welding, the time limit for the on-site stay in the factory environment is detailed. As well as the detailed conditions of the moisture absorption test.

(1). The normal test must be carried out according to the standard conditions in the example, or according to the commonly known diffusion activation energy of 0.4-0.48eV. After the test sample has been subjected to moisture absorption in the front section and reflowed in the rear section, once failures such as damage or poor electrical properties occur, further verification must be performed according to the "acceleration equivalent" condition on the right side of the table. Normal tests cannot be used Such acceleration conditions. The time-consuming of this kind of accelerated test can be flexibly changed according to the characteristics of different molding materials and encapsulating materials.

(2) The "Biaohuai Moisture Absorption" time is actually the "Manufacturer's Temporary Exposure Time" (MET) before the PCB semiconductor manufacturers baking dehumidification and bag storage, and after it is removed from the bag in the distributor’s facility If the exposure time does not exceed 24 hours in total, it can be included by default. When the actual MET is less than 24 hours, the moisture absorption time can be shortened, that is, when the condition of "30 degree Celsius/60%RH" is adopted, the moisture absorption time can be shortened to 1 hour. But if it is 30 degree Celsius/60%RH, where the MET is 1 hour more, the moisture absorption time will also increase by 1 hour. Once! ^ 2 Ding exceeds 24 hours, its moisture absorption time should be increased by 5 hours.

(3) Once the PCB supplier feels that the product is risky and unsafe, it can also extend its moisture absorption time.

(2) Reflow of the back section

When the sample of the seal to be tested is taken out from the temperature and humidity box of the previous test for 15 minutes, but not more than 4 hours, the sample must be carried out in accordance with the detailed regulations of Table 5-2 and Table 5-1. Reflow exam, and a total of three exams have to be passed. The interval between each reflow can not be less than 5 minutes, nor can it exceed 1 hour. Once the sample is taken out of the temperature and humidity box, if the reflow is not completed within the specified period of 15 minutes and 4 hours, the batch number of the sample must be re-baked and re-absorbed according to the aforementioned method.

PCB seals that have completed all examinations must first be visually inspected under a 40x microscope to observe whether they are broken. Then, conduct electrical testing and pass judgment on all samples according to the acceptance data in the catalog or the existing specifications in the factory, and finally use C-SAM to conduct internal rupture analysis.