How to control the PCB SMT soldering quality and lifetime of the Intensive LED display modules
PCB SMT soldering quality control of the intensive LED display modules
More and more commercial businesses are using LEDs as display billboards, it has led to increasing demand for intensive LED display modules in recent years. Meanwhile, it also brings more opportunities and challenges to PCB SMT soldering manufacturers, because the number of the pads on the dense LED display module is too large, and there is only one kind of pad on the top layer of the PCB board, that’s the LED pad and the numbers can be 1000-10000 PCS or even 20,000 PCS, all the other component pads are on the Bottom layer. This is not a simple soldering process as the LEDs are arranged in a dense array, and the spacing between the LEDs is close to zero. Some SMT soldering manufacturers may find some LEDs are blind when they do the power-on test after PCB SMT soldering finished, or the LEDs are all on before shipping, but there will be a few of them go off when customers received. However, the most headache is that it’s difficult to rework even if we find out the issues, because of the very limit spacing between the LEDs, and it is too difficult to rework it with a soldering iron, “hot air gun” maintenance will cause new problems. How to solve such kind of problems? Tree Technology will share some SMT production soldering experience, we found out there are two main reasons:
1- Stencil quality: when there are common BGA and QFP package components on a PCB, we will select electrolytic polishing as the surface treatment, but the stencil quality is the key to the solder the dense LED modules. Because the solder paste will be attached on the hole walls when it is printed on the ordinary stencils, the adhesion of the solder paste will directly affect the thickness of the printed solder paste, this has led to the failure of controlling the soldering quality. We suggest to use nano-steel stencil for soldering the LED modules, nano-coating makes the stencil “hole wall” super smooth, comes with superhydrophobicity, no residual tin, repels solder paste – reduces the adhesion of other substances onto the stencil, excellent release effect, perfect printing effect and the solder paste volume is rather even.
2- Solder paste printing quality: Many factories check the quality of solder paste printing manually, they may find out the tin leaking in a certain area, but it’s difficult to notice a certain one pad is lacking paste among thousands of pads and it can’t detect the thickness of the solder quickly and effectively, that’s why some of the LEDs don’t shine because the “tin leaking” cause false soldering/open circuit; if the solder paste is very tin on some pads, it may work during the power on testing before delivery, but there is the possibility that during the shipping period it turns out false soldering because of shaking. We are using online AOI testing after stencil printing to avoid such trouble, it can effectively detect all the problems: insufficient or excessive solder paste, paste and pads are poorly overlapped, short circuits between pads caused by solder paste.
Remarks: We have 6 SMT reflowing soldering lines, 4 DIP wave soldering lines (3 of them is lead-free type), AOI inspection, X-Ray inspection, etc., Quick turn prototype PCBA: 1 working days, Production order: 2 working days.
We provide one-stop service: PCB fab + PCB assembly + component sourcing.
Discount for the first order:
50% discount for bare PCB based on PCB+PCBA service ( prototype bare PCB turns out within 8~24 hours, ≥6 layers and HDI board not included)
How to promise the lifetime of the LED display modules
The reliability of LED products is one of the most important signs used to estimate the life of LED products. If the LED is chemically reacted or corroded by the surrounding environment, the performance of the LED is degraded. It greatly shortens the lifetime of the LED products. However, in most different environmental conditions, LED products can continue to work generally.
In order to avoid corrosion of the LED, the best way is
1- Check the LED components are damaged or not before SMT placement.
2- Avoid LEDs approaching harmful substances. Even a small amount of harmful substances can cause LED corrosion.
3-LEDs should be less exposed to corrosive gases during SMT soldering and especially should be protected from sulfur.
The followings are some LED accessories that may contain corrosive substances.
7-Sulfur-containing vulcanized elastomer
If these hazardous substances cannot be completely avoided, we suggest using LEDs with higher corrosion resistance. However, keep in mind – limiting the effects of corrosion, depending on the concentration of harmful substances.
Even if you choose LEDs with higher corrosion resistance, you should minimize the exposure of these LEDs.
Generally, heat, humidity, and light can accelerate the corrosion process. However, the most important factor is the concentration level and temperature of harmful substances. Limiting these two will be the most effective way to protect LEDs.