Thursday, March 12, 2009

LED Manufacturing Process

There is a few selection on the process for LED die bonding avialable in the HP LED manufacturing.

Die bonding Process for LED manufacturing

1. Silver Epoxy process
2. Direct Eutectic process
3. Flux Eutectic process
4. Flip Chip G2G process
5. Soft solder process

Silver Epoxy LED Die bonding
In the market, the common process is Silver Epoxy process as I can see 95% of the people in the world is using this process. As for Hi power LED more than 1 Watt, most of the people will use high silver content epoxy, but the silver content can go up to 70% which is very high already, Silver epoxy can be dispense or stamping.

Hi Power LED can enjoy certain period of life time base on silver epxoy, but if the LED is running at high current, the silver epoxy may not be the best process; as the silver epoxy will have certain limitation in the heat transfer.

The concern with epoxy is reliability. We have not found epoxy material that does not crack under automotive-like stress condition, although in terms of thermal conductivity, it could be quite similar to Au/Sn solder. Some LED vendors do use epoxy for attaching LED substrate onto heat sink, but they suffer in thermal performance.
The process is simple, material is cheap.
The UPH is 14,000 - 16,000. An hour for certain package if you use the latets High speed Die bonder AD830 series.

Direct Eutectic process
The main attractions of Au/Sn process are in its excellent reliability and its high thermal conductivity. The drawback is of course the comparatively high cost. But for LED based automotive forward lighting, which is still limited in the luxury segment, quality and performance is everything and that is the main reason we see people running with Au/Sn despite of the cost. The process is some time material related, the bonding time is one of the bottle neck for machine UPH typical UPH is 3,000 to 5,000 depending on die size. The expensive Forming gas is needed.

Flux Eutectic process
The problem with flux eutectic Au Sn process is the possible contamination of the LED source as flux evaporates. There are so called "low-flux eutectic paste" in the marketplace claimed by various vendors. We are still having queries on such claim. This can have a simpler process than Eutectic process. Machine UPH can be up to 14,000.

Flip Chip process
A gold bump has o be made on the substrates and special plated bump pad has to be made at LED side. Flip Chip machine requires high accuracy +/- 10 microns and not suffcient high in UPH, typically an UPH around 4,000-6,000. So this is a expensive way for LED manufacturing.
Only less than handful of people using this process for LED manufacturing. Typical sucessful company is Lumileds of Philips Group.

Soft solder process
Traditionally, the soft solder can be used for high power device application especially in the TO220 high power device. Why there is no one working on soft solder LED so far? The main concern with soft solder is the placement accuracy. +/-100um-200um seems to be normal for such process. One of the European supplier claims that their soft solder process can achieve +/- 37.5um @3 Sigma. This is still not good enough for the automotive forward lighting application. It may be sufficient for other LED products. Soft solder is much more expensive than silver epoxy and there is not many people using this process. As There is as this is Blue ray absorption by the soft solder and the solder will be delaminated after prolonged blue ray energizing effect!

Cost Comparison est.
1. Silver Epoxy process as 1
2. Direct Eutectic process 3
3. Flux Eutectic process 1.3
4. Flip Chip G2G process 4
5. Soft solder process 2

Distribution of Application est.
1. Silver Epoxy process 80%
2. Direct Eutectic process 1%
3. Flux Eutectic process 15%
4. Flip Chip G2G process 2%
5. Soft solder process <1%
6. Other process 1%


meng said...

Very informative for electronic industry. Thanks for sharing.

Anonymous said...

Meng, I hope that you can give us some of your comment!
By the way I left two SMS in your Hand phone for dinner on Thursday, but may be you did not get it! Probably next time we can share our comment on the LED/Hi Fi/Food/ Mong Kong/Canton-i/ stuff, By the way what kind of LP you need to me buy for you in HK?
let me know!


meng said...

Sorry Fever, My HP not activated for roaming that I can't return your sms. I will activate it soon.
Your info on DA methodology is much better than me as I am not aware of "soft DA". Sure, we can 吹水 further your next trip to Penang. mengee.

Anonymous said...

Hi Meng, I know that one of the largest equipment suppliers had already patented this as on their die bonder, and I can share with you the technology next time I appear at Penang.