The analysis of high consistency of LED module lamp bead

LED module is ： mount a single lamp bead on a copper or aluminum substrate to form a high power LED lamp.

Recently, our engineer found the lamp bead height difference is bigger based the analysis of the LED module, according to this phenomenon, we respectively tested  the client supplied module and our module about the aspect of lamp bead height , and comparative analysis from the LED lamp bead to all the module production craft processes, summarized possible factors caused in SMT in substrate lamp bead highly inconsistent problems .

The LED module that client supplied .is arranged and distributed in a font pattern, with a total of 24PCS lamp beads.In order to ensure the comparability of test data, a total of 24 pieces of lamp beads were all strictly tested . The test results are shown in Table 1.

Table 1.LED module bead height test data

Considering the influence of the flatness tolerance on the substrate surface, the solder resistance surface at the bottom of each lamp bead was selected as the test datum.we can know From the test data, it can be seen that the minimum and maximum height of the lamp bead in the client supply module are 3.018mm and 3.361mm, and the height difference is 0.343mm.The minimum height of the UVLED module lamp bead of Bytech electronics company is 2.378mm, the maximum is 2.475mm, and the height difference is 0.097mm.The consistency of lamp bead height of our module is much better than that of client purchased module themselves .According test and  analysis, the main reasons for the inconsistency of module lamp bead height are as follows

1. SMT welding process

X-Ray scan images of the customer supplier module and our module are shown in Figure 1:

·      Figure 1. Module X-Ray scan

From the X-ray scan, it can be seen that the cavity rate of solder paste layer of the client-supplied module is relatively high, up to about 20%, while that of our module is less than 5%.This indicates that the uniformity of the solder paste layer of our module is better than that of the client-supplied module, so the tolerance of the solder paste layer is smaller than that of the customer-supplied module. On the other hand, our SMT vacuum reflow welding process reduces the influence of voids on the photothermal characteristics and reliability of LED lamp beads to a large extent

2. Ceramic substrate

On the LED lamp bead support, the copper-plated ceramic substrate is used, which is different from the enclosure dam structure, as shown in Figure 2.

·      Figure 2. Structure diagram of lamp bead bracket

The step structure is used for lens positioning and installation in the design of the enclosure

The step structure is usually used for lens positioning and installation in the design of the enclosure dam of the client supply lamp bead bracket. The enclosure dam of bytech bracket is round cup with simple structure. On the making craft of ceramic substrates, the steps increase the highly difficult to achieve precise control, and excist design value of larger tolerance, the steps structure need the craft process to achieve ideal height can only adopt by milling or edm, however in this two kinds of processing methods for post-processing greatly increases the production cost of lamp bead bracket, most manufacturers would not consider it.The most choice support without step surface, which simplifies the technological process, and the height of the dam enclosure can be effectively controlled by limiting membrane

3 dispensing process

After the lamp bead dissection, it was found that the glass lens and bracket were bonded together by glue for the client supplied module lamp bead, and Bytech company bonded them by metal to metal, as shown in Figure 3.

The step structure surface of the client supply lamp bead is small. In the process of dispensing, some glue will flow into the inside of the dam, and it is difficult to ensure the consistency of the amount of glue on the step surface of each lamp bead.In the process of covering the glass, due to the influence of the gravity of the lens itself, part of the glue will be squeezed into the enclosure dam, so in the process of dispensing the glass will lead to the difference in the height of the whole lamp bead.Bytech lamp bead adopts full-inorganic encapsulation packaging structure, which effectively avoid the influence of other bonding media on the height of the lamp bead. Meanwhile, compared with organic materials (glue), the inorganic lamp bead has better UV resistance, so as to ensure that the lamp bead will not fail due to the physical and chemical reaction of organic materials under the irradiation of violet light in long-term use.

4. Lens

During the manufacturing process, the lens will have its own tolerance, about ±0.02mm, which is an unavoidable factor at present.Due to the small tolerance of the lens itself, the overall height of the lamp bead can be ignored.

From the comparison and analysis of the LED module surface lamp bead height data, it can be seen that the structure and vacuum reflow welding process of Hongli Bytech electronics full-inorganic encapsulated UV LED ensure the consistency and reliability of the module lamp bead height size, which is far superior to the existing products on the market.