How an Asian display manufacturer successfully improved its yield up to 100% in production of small SMD LED carrier boards in shortest times.
They are the brightest stars on Times Square in New York or on skyscrapers in the Far East – huge LED-panels as we know them from big-budget science fiction movies are not being manufactured in one piece: they are made of countless small PCBs which are being put together to assemble each screen containing thousands of individual lighting elements.
Those small boards have dimensions of only a few inches but carry thousands of pixels, each one comprising several small SMD LED components. One square meter of such a display can contain well over 3 million LEDs.
Higher quality – lower rejection rates
There are only a handful of manufacturers in the world these days who are able to employ the small SMD LED technology for large format displays. One of them confronted Finetech with the following issue: production process of its large format displays bore manufacturer failures of individual LED components which had not passed the electrical test. One should note that with so many LEDs, even under high-precision manufacturing conditions, individual defective pixels are part of natural output fluctuations and tend to be the rule rather than the exception. So the challenge was to bring the yield closer to 100% in order to sustain resources.
Finetech together with the customer successfully developed a multi-stage repair process which would allow for restoration of individual pixels in such a way that adjacent components stay unaffected. The goal: no longer reject whole carrier plates because of insular LED defects.
It became clear already in 2009 that components as small as 220 µm x 120 µm are light in weight, thus hard to handle, when Finetech was the first in the market to present the solution for this component size. Ever since the handling process has repeatedly been optimized and improved and is being successfully used now for rework of LED displays.
Rework process steps:
- Removal of SMD LED component
- Residual solder removal from circuit board
- Applying new solder paste
- Precise component placement
- SMD LED component soldering
- Avoiding damaging or disturbing adjacent LED components during the rework cycle
- Compensating thermal drift in the board material during soldering and de-soldering
- Reproducible dispensing of solder paste in 100 µm dots
Development is a process of multiple steps
Quick reaction and customer-oriented approach are already part of Finetech’s DNA. That is why we have adapted and developed a solution in no time: samples we had previously received were one-sided PCBs, but those brought to our laboratory in Berlin by the customer later on were actually double-sided.
Due to our 25 years of experience in the field, we could quickly adapt the developed solution for that display manufacturer from contact heating to hot air heating. This is a completely new approach optimized together with the customer, where new challenges were to be expected. Under hot air heating the circuit board is subject to different kind of expansion compared to contact heating, that is why the tools as well as the whole rework process had to be readjusted.
The biggest challenge in the process lies in the tiny dispense points with the diameter of 100 µm which have to be dispensed reproducibly. For that Finetech has used a stamping tool in the form of a suitable transfer pin to apply fresh solder paste very precisely and thereby convince the customer.
Improved production in a few days
Our fully-equipped application lab, in-house tool manufacturing and years of experience in SMD rework systems helped to present a reproducible solution in only four days. As a result, the customer has not only purchased the rework system, but also got a fully developed process and gained a strong and trusted partner.
Even today Finetech is the only machine manufacturer in the world who can map a secure and reproducible rework process for small SMD LEDs entirely on one system which, in turn, optimizes production yield.