I cannot see the wave profile as it is not attached.
One thermocouple needs to be glued to the plastic lense of the LED to check what the top preheaters are doing.
Possible problems, some arriving with the introduction of SAC alloys.
1. The plastic through which the leads exit the LED body maybe reach the heat distortion range of the plastic, which is much lower than the melting temperature. The seal may be broken. This is a common problem with plastic headers where the pins are compatible for PB-free but the PTE material wasn't. Since LEDs are soldered to a ground the heat needed for a good fillet may damage the part.
You may have to adjust the profile to get an acceptable hole fill versus enough heat to get 100+ solder joint that you would prefer to have.
2. I've had LED failures that were the result of oxidation of the metal elements prior to the actual manufacturing of the LED.
We had to make a tester where we plugged the LEDs into socketed test board and let them run all night (not sure exactly how longthe test was) and found failures without soldering nor cleaning. With the evidense in hand we purged the parts and had the vendor do a corrective action and got the process back in control eliminating the need for the test once we got good parts.
3. You didn't mention what type of preheaters you had on the wave. One of the things you should have at wave are Durastone or Durapol (high temp/ESD pallet material) blocks, some milled to have two sides to keep the block off the part but blocks an IR heat and lowers convection heat for ONLY the sensitive part. Lowering the heat to improve quality of one part can cause problems with other parts like power coils, power modules and large electrolytic capacitors. Another good type of protective cover to have is a square of this material milled out to form a pocket in the center to cover BGAs during the wave solder.
These are placed over BGAs for process for certain processes: thin pallet base transfers alot of heat or where long contact time and high heat is needed for other areas and parts of the board.
Hope this helps.
4. Check to see if the lead spacing of the LEDs match the hole spacing. If there is a preforming process going on then there could be stress related issues contributing. The variance could be between the people preping and installing the parts and over clinching the leads to either keep them straight or to hold them flush to the board because the pallet design isn't doing the job.
The leads must have .060" - .080" lead protrusion to wick up the solder. Anything more than a 45 degree clinch works against the wave process.
John Goulet
MFG/Process Engineer
----- Original Message -----
From: "Don McFarland" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, November 18, 2010 10:52:14 AM
Subject: Re: [TN] Led Failures Please help
Bu chance, Is there any CC added after test that requires a UV cure process?
Sent from my iPhone
On Nov 18, 2010, at 8:46 AM, Michelle <[log in to unmask]> wrote:
> No this is all No clean
>
>
>
> ----- Original Message ----
> From: David D. Hillman <[log in to unmask]>
> To: [log in to unmask]
> Sent: Thu, November 18, 2010 10:16:42 AM
> Subject: Re: [TN] Led Failures Please help
>
> Hi Michelle! Are you cleaning the LED assembly/components in any manner?
> LEDs do not play well with many cleaning processes or cleaning
> chemistries.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Michelle Masaitis <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 11/18/2010 07:41 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Michelle Masaitis <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] Led Failures Please help
>
>
>
>
>
>
> - the through-hole LED in question is made by company "EOI ", and their
> part number is "EOZ-ZARNCD0-DG " (s
> - according to the component spec sheet (enclosed), the maximum
> temperature for the component is 260℃
> - the maximum temp and wave contact time we initially used is 249℃ ,
> 4-6
> seconds. We saw some defects after first pass, usually about .2%, but one
>
> month as high as 1.5%. After successful testing, there were then some
> latent defects that occurred at our customer or their end customer. The
> defects are erratic, sometimes the LEDs work, and sometimes they don't
> - the supplier recommended a lower temperature and shorter exposure
> profile
> so we used SAC305 solder with maximum temp of 244.4℃ and 3 seconds.
> There
> were no defects after first pass and testing, but again we had some latent
>
> defects occur at customer
> - for reference, we run many similar LED from other manufacturers
> (OSRAM&Lumiled, also spec at 260℃) at temperatures of 251℃ and 4-7
> seconds
> and see no such problems.
>
> Attached is a wave profile.
>
> Please let me know if you seen a similar issue and what caused it.
>
>
> Thanks
>
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