How to choose the right SMD LED

    We have got to know about  the detailed process of SMD LED package,with the led development , there is almost no difference of LED Encapsulation Process,but why the price is so much different among them? Take  2835 SMD LED Modules for example,Some one sells 9RMB/K,and the others sells 40RMB/K,even some much more ? then whats the quality difference about them?
    First we need to understand that the LED has been fully industrialized now,SMD LED price are main based on the following factors:
  1.The material cost of product,these include: LED chip,LED frame,LED bond wire, LED glue ,LED phosphor powder and some production auxiliary materials, such as packaging materials and taping etc.
  2.Production efficiency: The production efficiency here is mainly reflected in the automation equipment, its more efficient in the big plant while low in small factory,and only a few key operations will use automation,many of the non-critical processes are manual, or semi-automatic.
  3.Brand effect,The most obvious example is the difference between Cree and domestic chip factories,there is nothing for discussion.
 
    Material cost is the most important ,Let's follow the steps to get to know the process and material about the Encapsulation.

LED Chip:
       As the Light Source of LED SMD,the quality  of LED chips directly decided the main performance parameters of the LED SMD, and there is quite different from all the Package factory,take SMD 2835 of 0.2w for example, there have many type such as : 9×15mil，1016,1017,1020,Obviously the same chip factory, the smaller the size, the lower the price.So the question comes, since small and large size are 0.2 W, of course we choose the cheap one, then what is the advantage for big one?
      To measure the parameters of the SMD LED except for power, there is a very important parameter called brightness.As we know,LED chip most are constant current,Under the same current density, the bigger size of chip, the higher brightness of the whole chip.then that’s why some brightness is 20lm ,and the other is 24lm.of course there is other difference except the brightness ,we will talk in the future.

LED Frame:
    Frame plays an important role in LED SMD of heat conduction and import the current ,the heat source of LED SMD is PN junction ,also as LED is cold light source,it can’t radiate in the form of heat,then frame is the most important as the medium of PN junction for heat conduction.But there is big difference about the frame price ,then how we choose?
    1.Material of Frame,now there are iron frame,brass frame and copper frame and so on ,and iron frame is the cheapest.But Whether it is electric conductivity, thermal conductivity, ductility or rust status, iron stands are the worst,brass type comes the second and copper is the best.Here need to pay attention to the ductility of material,when LED is used,frame will continue to expand,If the ductility performance is not good ,then will cause  internal and colloidal detachment,wiring joints broken,also joint connected the external and PCB plate's solder crack or even disengage.
    2.Coating thickness,as we know,no matter what kind of frame material is used, plating is necessary.The usual process is silver plating,but the thickness is different, such as :40、60、80、100u"（40u"=0.001mm),the advantage of coating thickness and uniformity can be conductive homogeneous,high conductive efficiency will better for wiring ,also price is high.
    3.The plastic part of the bracket light cup is different,the plastic part should satisfy low water absorption,strongly bonded with silica gel,good condition of good reflection effect.That’s why we use PPA and PCT,also big and standard factory will use all brand new material, but some other factory may use the regenerative plastic ,waste materials, recyclable materials ,this will be bad for frame quality.

Bonding wire:
     Bond wire have function,one is for electric conduction,connect the chip and the  conductive layer of frame.Another function is heat conduction,transfer the heat of the LED chip.But there's a big impact on the led that many people don't notice,the bond wire will affect the light of led,even will change the color temperature brightness and other parameters.

     The bond wire is made of gold wire, alloy wire, aluminum wire, copper wire and so on,also according to the thickness it divide into 0.7、0.9、1.0、1.2 mil etc.The gold wire is the best for electrical conductivity, thermal conductivity and ductility,of course price is high.And a lot of aluminum wires, copper wire should over strike diameter of the wire to overcome the problem of the wiring joints fall off.Some type even up to 6mil,but the consequences of bold bond wire is out of the low brightness, light color drift is serious and so on.

Glue Preparation:
     It is to mix the corresponding phosphor powder and packaging glue evenly according to the customer's requirement.Also the use of different phosphors and glues have a great influence on the led.
Phosphor powder greatly affect all optical performance of the led including brightness, color temperature, CRI, life span and so on,then how to identify whether it is good or not?

    1. Conversion efficiency blue light is high,now most popular white light led actually shine blue light,only the blue light stimulate phosphor powder to make it into red, yellow，and the white light actually is the mixed blue light.we also can check it out from the test report from integrating sphere.So the higher the conversion efficiency of phosphor, the brightness of the lights will be higher.
     

                                            

    2.When the Phosphor powder in the process of conversion to blue light,it is actually a process of constant consumption of itself.In another word,As the longer of phosphor used, its conversion efficiency will be lower,  Finally  the white light of the led would slowly turned into blue light.

     Except phosphor power, LED encapsulation glue also is very important ,the main function of glue is as follows:

    1.Packaging glue should bond with light cup completely, isolated from the air and water vapor,this will completely protect the led chip and  silver coating.Good glue  tightly sealed, low expansion coefficient and low water absorption,it also won’t be crazing and falling off even for long term using.but the bad glue will .

    2.Glue should well mixed with phosphor also should have the function of precipitation resistance  for phosphor in short time.as we know , phosphor can’t really dissolve in water,just in suspension.but is in this situation ,if phosphor precipitate faster,it will be result in lot unevenness of light.Bad glue not only need adding Anti precipitation agent but it contain a large amount of solidified grain,this will affect the light of led.

Sorting：
     As there are many factors which affect the led photoelectric performance,there will be subtle different even using same material an under same process.So sorting is the most important for testing the led photoelectric performance.Sorting machine classify according to led voltage ,CCT，brightness and so on .This is what we often call the bin, and strict bin can guarantee the consistency of led from the factory.
     There are different standards about the bin and voltage  Classification for every factory,92% yield Is normal (the rest led are not all fail or out of light,just CCT and voltage are not same standard some different. )But some factory want to reduce the production cost ,they only delete the led which out of light,this will lead lights appear different color like red, green and so on.

       From above difference,we can see that one small led play an important role.Based on this difference,we divided LED packing factory into three classes:
      1.All materials are used very well, the process is also controlled very strict, do not hesitate to make the high-quality goods.Basically,they are famous factorys, such as Cree, Epistar, etc.
      2.Use better materials in some of the key parts and in some non-critical parts with slightly cheap raw materials.This kind of factory pursues short barrel and cost performance.But it will be very difficult to control ,as it need long term testing and exploration,also the standards from each factory are quite different.
     3.The last type pursues low-cost products,which is cheap then what to use ,following the standard of the most simplest process.there is no research value for this .
     One of the simpler ways to distinguish between these three types of factories is the price.Since LED industry development till now,there is no windfall profit for most factories.So under reasonable profit and based on high price ,the materials used in led will be much better,of course relative test is necessary.
 

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