Abstract: This article mainly introduces moisture absorption and humidity control in the production process of LED. Light-emitting diode products have gradually become the darling of photoelectric display field with the advantages of low consumption, high life and good weather resistance. Especially in the field of solid-state lighting in recent years, high-power LEDs have been increasingly favored by the industry. 0 hrs 24 hrs 48 hrs 72 hrs 96 hrs 168 hrs 336 hrs 500 hrs Smd 0 2.6 ‰ 3.5 ‰ 3.7 ‰ 3.9 ‰ 4.2 ‰ 4.25 ‰ 4.3 ‰ Top 0 3.2 ‰ 4.2 ‰ 4.7 ‰ 6.0 ‰ 6.5 ‰ 7.0 ‰ 7.5 ‰ 1. Shorten the process time of the product, and strictly control the placement time in the air after molding. 24 hrs post-packaging Product over tin furnace (180pcs) 60 ° C Sealing and peeling force is normal, no change in upper and lower belts, reels, etc. There is a dead light phenomenon 80 ° C The sealing and peeling force is slightly reduced, the upper and lower belts are not deformed, and the reel is slightly modified. No dead light 100 ° C The sealing and peeling force is slightly reduced by about 5g, and there is no deformation of the upper and lower belts, and the reel deformation No dead light 125 ° C Sealing and peeling force is slightly reduced by about 10g, with slightly modified upper and lower, reel deformation No dead light It can be seen from the above test that when the product is subjected to high temperature after moisture absorption, delamination phenomenon may occur and a dead light may appear. Proper temperature baking is a more effective method. In addition, auxiliary means such as vacuum packaging can also effectively prevent the light-emitting diode from absorbing moisture. Editor: China Lighting Network / Leaves Canon Camera USB Cable,Canon Digital Camera USB Cable BETOP TECHNOLOGY CO.,LTD , http://www.betopparts.com
LED products are divided into: dot matrix digital tube, lamp, smd, top view, side view, high power and many other varieties, but all of these varieties have a common point is the presence of non-hermetic packaging of resin and stent. Therefore, they are all moisture sensitive components, and the moisture sensitive components are exposed to the elevated temperature environment during reflow soldering. The moisture inside the resin surface mount device (SMD) will generate sufficient vapor pressure damage or Destroy the component. Common failure modes include internal separation (delamination) of the resin from the chip or leadframe, wire damage, chip damage, and internal cracks that do not extend to the surface of the component. In some extreme cases, the crack will extend to the surface of the component; the most serious case is the component bulging and bursting (called "popcorn" benefit). IPC - The Electronic Industries Association of the United States has developed and published IPC-M-109, a moisture sensitive component standard and guidelines manual. It includes the following seven files:
· IPC/JEDEC J-STD-020 Hygienic Integrated Circuit (IC) SMD Moisture/Reflow Sensitivity Classification · IPC/JEDEC J-STD-033 Wet/Reflow Sensitive SMD Handling, Packaging, Shipping and Use Standards · IPC/ JEDEC J-STD-035 Acoustic microscopy method for non-hermetic package components · IPC-9501 Simulation of assembly process for printed wiring board (PWB) for evaluating electronic components (preprocessed IC components) Method · IPC-9502 PWB Assembly Soldering Process Guide for Electronic Components · IPC-9503 Classification of Moisture Sensitivity of Non-IC Components · IPC-9504 Evaluation of Assembly Process Simulation Method for Non-IC Components (Preprocessed Non-IC Components) Among IPCs /JEDEC J-STD-020 defines a moisture sensitive component, a classification procedure for non-hermetic packaging made of moisture permeable materials such as plastics and resins. The procedure includes exposure to reflow soldering temperatures followed by detailed visual inspection, scanning acoustic microscopy, cross-section and electrical testing. IPC/JEDEC J-STD-020 also divides moisture sensitive components into eight grades, namely:
· Class 1 - ≤ 30°C / 85% RH Infinite shop life · Class 2 - ≤ 30°C / 60% RH One year workshop life · Class 2a - ≤ 30°C / 60% RH Weekly workshop life · Level 3 - ≤ 30°C / 60% RH 168 hours workshop life · 4 grades - ≤ 30 °C / 60% RH 72 hours workshop life · 5 grades - ≤ 30 °C / 60% RH 48 hours workshop life · 5a grade - ≤ 30 °C / 60% RH 24 hours shop life · 6 levels - ≤ 30 ° C / 60% RH 72 hours workshop life (for level 6, the components must be baked before use and must be specified on the moisture sensitive caution label Time limited to reflux).
Light-emitting diodes generally belong to the three levels of 2a, 3, and 4, of which smd belongs to level 3, and top view and side view belong to level 4. Therefore, the corresponding production process time is to be controlled within the scope of its requirements.
At present, smd products including top view and side view are deadly in the industry when customers are reflowing, and moisture absorption control is also an effective way to solve this problem.
According to the author's weighing test, the moisture absorption of the LED is analyzed:
This roughly determines the moisture absorption ratio. It is even more necessary to control the process and customer usage time, and make adjustments to the process of the corresponding moisture absorption products.
2. Baking and dehumidifying treatment should be carried out before the production of moisture-absorbing raw materials. The time/temperature of the baking is determined by the characteristics of the material.
3. Control the temperature/humidity of the production site and place the semi-products in a moisture-proof cabinet.
4. The product is baked and dehumidified.
5. Vacuum packaging the product.
6. Bake and dehumidify before use for long-term product placement.
Among the product packaging and baking, IPC/JEDEC J-STD-033 provides the recommended method for handling, packaging, shipping and baking moisture sensitive components. The focus is on packaging and preventing moisture absorption - baking or de-wetting should be the ultimate method of use after excessive exposure. Dry packaging involves sealing the moisture sensitive element with a desiccant, humidity indicator card and moisture sensitive caution label in a moisture barrier bag. The label contains shelf life over a range of specific temperatures and humidities, exposure time after opening the bag, details about when baking is required, baking procedures, and the date the bag is sealed. Level 1. Drying prior to bagging is optional, bagging and desiccant are optional, and labeling is not required unless the component is sorted to a reflow temperature of 235 °C. level 2. Drying before bagging is optional, bagging and desiccant are required, and labeling is required. 2a ~ 5a level. Drying before bagging is required, bagging and desiccant are required, and labeling is required. Level 6. Drying before bagging is optional, bagging and desiccant are optional, and labeling is required.
Of course, due to the packaging bag, we can use the method of dehumidification or baking for the drying of the product. 1. Dehumidify at room temperature. Use a standard dry packaging method or a drying oven that maintains 25 ° C ± 5 ° C and humidity below 10% RH and places 5 times the air exposure time to restore the original shop life. 2, baking. There are some recommended methods of baking for pre- and post-drying packages based on grade and package thickness. Pre-bake is used to prepare the components for dry packaging, while post-baking is used to re-recover components after the shop has reached the end of its life. Please consult and follow the baking time/temperature recommended in J-STD-033. Baking temperature may reduce the solderability of the solder pad by oxidizing the solder pad or causing excessive intermetallic growth; in addition, if the product is packaged and packaged after dehumidification, it is necessary to consider the baking on the package. The impact of sealing.
The pre-baking recommendations for IPC's dry packaging are:
1. Before packaging, the package thickness is less than or equal to 1.4mm: for the 2a ~ 5a level, the baking time range of 125 ° C is 8 ~ 28 hours, or baking at 150 ° C for 4 ~ 14 hours. The package thickness is less than or equal to 2.0 mm: for the 2a ~ 5a grade, the baking time range of 125 ° C is 23 to 48 hours, or baking at 150 ° C for 11 to 24 hours.
2. After the shop life has expired, the package thickness is less than or equal to 1.4mm: for the 2a ~ 5a level, the baking time range of 125 ° C is 4 to 14 hours, or baking at 40 ° C for 5 to 9 days. Package thickness is less than or equal to 2.0mm: For 2a ~ 5a grade, the baking time range of 125 °C is 18~48 hours, or baking at 40 °C for 21~68 days.
3. Tape and reel packaging products have also been tested in several groups. The baked smd products are first placed at 30 ° C / 80% RH for more than 336 hours.