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smd led storage

Views: 6329

#61389

smd led storage | 18 March, 2010

hi, lately I have problem with smd leds.After reflow 2-4% of leds are broken.I think , that reason is bad storage of components, because in our stock the tape with leds have not Moisture Barrier Bags.My question is ,how you storage components, which are moisture sensitive?

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#61390

smd led storage | 18 March, 2010

I would recommend doing a google search on smt dry box. There are several supplies of them. We supply them also from http://www.manncorp.com

Thanks,

Chris

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#61391

smd led storage | 18 March, 2010

The standard J-STD-033B.1 addresses how to store moisture sensitive components. A dry box is a good, convenient way to store MSDs, but there are other methods to consider which are outlined in the standard.

Are you sure that the problems are caused by moisture? Even if they are not, it is good practice to comply with the J-STD-033B.1 standard. Be sure you get the .1 version, as it has a number of updates. You can get the standard through IPC, JEDEC, SMTA, etc.

Dean

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#61392

smd led storage | 18 March, 2010

Is your peak reflow temp exceeding the LED spec? We store our SMT LED reels on the rack with the rest of the discreets and have never seen this issue...

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#61393

smd led storage | 18 March, 2010

Hi, First check what the Moisture Sensitivity Level of the LEDS is....you may need to ask the LED manufacturer. Once you've established it is moisture sensitive then follow latest version of IPC JEDEC 33 spec. for storage of them and drying them if they are already over their open time. Maybe invest in a dry cabinet like those offered by Totech to take the hassle out of storing/handling moisture sensitive devices. Once you've eliminated moisture as a possible cause then double check the peak reflow temp that the device can withstand (again ask the manufacturer for this data...it is also called Peak Package Temp)and make sure they don't get near that temp in the reflow oven by fixing a thermocouple to the device body and measuring the actual temps it experiences in the reflow oven.. Good luck.

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#61400

smd led storage | 19 March, 2010

> Hi, First check what the Moisture Sensitivity > Level of the LEDS is....you may need to ask the > LED manufacturer. Once you've established it is > moisture sensitive then follow latest version of > IPC JEDEC 33 spec. for storage of them and drying > them if they are already over their open time. > Maybe invest in a dry cabinet like those offered > by Totech to take the hassle out of > storing/handling moisture sensitive devices. Once > you've eliminated moisture as a possible cause > then double check the peak reflow temp that the > device can withstand (again ask the manufacturer > for this data...it is also called Peak Package > Temp)and make sure they don't get near that temp > in the reflow oven by fixing a thermocouple to > the device body and measuring the actual temps it > experiences in the reflow oven.. Good luck.

Hi, most of leds in our productions are level 3.That means, that can use them to 168h after opening.We don't observe that.I make some tests - for example - divide equally a production lot.The first, use leds for not opened tape.For another part of lot, use leds, wich are opened 1 month ago.The resault is:no any defects in lot 1, and 2% defective leds in the lot2.All another conditions are equivalent for lots. Sometime, the first test is OK, and after several day a make second test and leds not blinking.... I think , that the reason for this problem is moisture in the leds.I want to use vacuum machine ( see attach) to pack tape before return to our store. What do you think about this idea??

regards,

Attachments:

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#61401

smd led storage | 19 March, 2010

Some things you have to be sure of... Can you guarantee the LEDS are DRY when you receive them ? They may be packed in dry bags but when was this done and has the LED distributor had them open at his site ? Using vacuum sealed dry packs is a good way to store dry devices....but don't seal devices that are not dry or over their open time. Dry Cabinets let you put devices in/out easily and I know that Totech has data for how their cabinets dry components. Use of dry cabinets is good for devices that are constantly on/off the placement machines. Dry packs good for longer term storage of dry devices. But you must follow IPC JEDEC 33 to guarantee moisture induced reflow problems don't occur. This spec accepts dry cabinets at 5% or lower can store most MSDs forever....get the spec and speak to a dry cabinet / dry pack sales guy and they'll advice on the regime you need to use.

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#61404

smd led storage | 19 March, 2010

Hi, do you know if your LEDs are moisture sensitive ? And if so what MSL level ? Surprisingly it seems that not all are, but some seem really sensitive. I imagine the differences are down to the plastics used and the LED manufacturing processes. I agree that peak reflow temp is also something that needs to be checked for the device, infact any moisture sensitive device.

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#61406

smd led storage | 19 March, 2010

Hi, most of them are MSL 3.There are MSL 4 and 2a.Most of defective LEDs are 3528 footprint.The thermoprofile is Ok??

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#61414

smd led storage | 19 March, 2010

Regarding your question about buying equipment to vacuum seal the MBBs, according to the IPC/JEDEC standard, "Full air evacuation is not needed or recommended; light air evacuation will reduce the packaging bulk and enhance carton packing. Excessive evacuation may impede desiccant performance and lead to MBB punctures."

All you need is a heat sealer. Just bake any overexposed parts, insert a desiccant pack and HIC card into the bag and heat seal.

Dean

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#61428

smd led storage | 22 March, 2010

Are you absolutely sure the problem is with the humidity? We had a problem with 3528 size leds, damaged by the pick and place nozzle because a 0.2mm mistake in the height measurement.

Also, we found that several suppliers are using fake desiccant bags. One such bag was damaged and little transparent balls came out of it. Just by curiosity someone checked and found that they are not desiccant at all, just pure plastic balls, probably some junk collected from somewhere.

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#61431

smd led storage | 22 March, 2010

Hi , I think that our problem is humidity, because when I use leds from new tape ( pack in MBB ) no any defects.After that, we put opened tape in our store.After 2-3 weeks I use the same tape with leds, and we have 2-3% defective leds.I make this test 2 way and the result is the same... But , thanks for advice , I will check nozzle settings i our P&P and leds size.

Regards,

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#61436

smd led storage | 23 March, 2010

Hi, It is very important to follow IPC JEDEC 33 specification for storage and handing of all MSDs. In many instances defects caused by excess moisture in packages is not immediately evident (pcbs may pass final test) but when pcb has been in the field for a short time the weakened package will start to degrade quickly and the device may fail. With LEDs you do stand a chance of seeing a problem (or not seeing it if it doesn't light up) but with other devices it may not be obvious. How many of the LEDs that worked okay will fail early in their life ?

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