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Fillet Tearing

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Dear all, Referring technical report from Vitronics Solte... - Mar 22, 2006 by

Bomb europe! ... - Mar 22, 2006 by

Joseph

#40548

Fillet Tearing | 22 March, 2006

Dear all,

Referring technical report from Vitronics Soltec, "Pad lifting, fillet lifting and fillet tearing issues in LF soldering". The use of LF solder alloys today has brought about a recurrence of this crack formation, called fillet tearing. There appears to be no cure this time; changing process parameters hardly provides any improvement. Therefore, crack in solder fillets, on PTH solder joints especially on primary side, are a common effect in LF soldering.

But the "baseline" from our customer is that , the solder joint cracks (or whatever they are called) it's not acceptable from them, unless if they are according to the IPC-A-610 definition of a "Hot Tear".

Since IPC standard do not mentioned above the fillet tearing, is anybody has any comment for the visual inspection criteria, or how to produce zero fillet tearing assembly ?

Best regards,

Joseph

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PIC

#40552

Fillet Tearing | 22 March, 2006

Bomb europe!

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Rob

#40555

Fillet Tearing | 22 March, 2006

Leave us alone, olive oil isn't the same as crude!

Defect of the month is... hot tear.

http://www.smartgroup.org/pdf/Defect01.pdf

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RDR

#40556

Fillet Tearing | 22 March, 2006

Good one Rob!

But you know we americans now need more oil and energy to process these leadfree boards so.......

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#40557

Fillet Tearing | 22 March, 2006

Rob, Very interesting The defect of the month that isn't a defect, that was a defect with Sn/Pb but isn't a defect in lead-free. I wonder if wave master Larry can solve the puzzle?

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RDR

#40558

Fillet Tearing | 22 March, 2006

I like the "if you can see the bottom" part! would that include Xray inspection?

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KEN

#40559

Fillet Tearing | 22 March, 2006

Find out the lead frame alloy. Cte mismatch can cause the same defect. Ran into this 3 years ago wave soldering with Tin-Copper.....okay, you caught me.

I admit it. Wavemaster larry told me about this and I'm posting it under my name. Shameful, I know. I'm just tired of living under his shadow. Forgive me?

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Rob

#40560

Fillet Tearing | 23 March, 2006

Is anyone else picturing a Homer Simpson lookalike in a lycra one-piece with WML emblazoned on it?

I wonder if controlling the cool down after the wave would help avoid this - it's something everyone does after reflow for joint formation, I've just never thought of it after the wave.

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Chunks

#40562

Fillet Tearing | 23 March, 2006

According to the original article, no. It is formed by the FR4 expanding and then contracting. So cooling it down faster would not help - in theory. We have not gone lead free yet, so take the above with a grain of WML. My question to those that have gone lead free (and WML) is, can you see this tear/crack under normal conditions, or is it something you need a X40 microscope to see. The original article also made it seem like this is a "non-problem". My concern is the inspectors after wave. If they can't see it, and this isn't a real problem, we keep running. Kinda like the contest between two people to see who can punch the softest. I always lose!

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Wave Master Larry

#40567

Fillet Tearing | 23 March, 2006

WEll Im hearing all this talk about leadfree nonsense from the engineering dept at my place of employment.Let me tell you Ive been looking at this stuff for 12 yrs and i think tearing of the filet is a normal part of the solder joint kindof like dross.everyones all worried about dross and such but i feel its the nature of the beast with wave solder.our second shift inspectors have eyes like hawks and they always seem to catch this stuff.same goes for those gull-leads that our ai dept places on the board.our inspectors seems to catch those as well.those gulled parts have a wrinkly appearnce but that has more todo with bad profiling.Again as i mentioned in another post Im acutualy looking to branch out in more of a consulting role.It seems like my threads that i post here seem to make alot of you less expereinced folks scratch their heads which is why i thought about this consulting thing.seems not enough of you think outside the box like me.Ill be posting more frequently in the future to all matters wave related and if anyones intrestid in my consutlation i can be emailed at WaveMasterLarry@yahoo.com i understand theres another fella here who has a website for consulting too and if he can do it why not me too?

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Gilligan

#40570

Fillet Tearing | 23 March, 2006

Wave Master and MoonMan, sitting in a tree S-O-L-D-E-R-I-N-G First comes dross Then comes fillets Then comes Consulting about the no-lead stuff

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Chunks

#40571

Fillet Tearing | 23 March, 2006

LOL!!!

I have over 20 years of this stuff. Should I be wearing a cape or have a spiffy name like Moon or Master?

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Rob

#40572

Fillet Tearing | 23 March, 2006

Sorry, Super Chunks is already taken.

http://www.hygro.net/joyprod.htm

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RDR

#40574

Fillet Tearing | 23 March, 2006

I think you're right Larry! I am going to put together a list of all my competitors and have you consult them!

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Chunks

#40576

Fillet Tearing | 23 March, 2006

So is Special Chunks! And really feel "special" when I have to deal with all the Larry's at my place of employment. Guess I'll just have to buy my own cape, but I still refuse to join the Super Adventure Club with Master Larry and Moon Man.

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Rob

#40578

Fillet Tearing | 23 March, 2006

Well, at least it gives you an option if you ever have a heavy fall & land on your head.

Could you not modify an ESD coat & add some copper welding rod to give it that flying in the wind look?

You could even decorate it with some disposable heal straps as tassles.

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#40579

Fillet Tearing | 23 March, 2006

Russ,

On a serious note it's impossible to optical see the bottom. The only way to verify is cross sectioning. Tin can't handle stress very well unless lead is added to make the alloy more elastic. We come back on the subject when the "field" starts talking I'm sure the message will be loud and clear. Some might actually see the bottom (sorry couldn't help being a little sarcastic).

Pat

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Chunks

#40582

Fillet Tearing | 23 March, 2006

I thought I already DID fall on my head and that's why I'm here.....

I think you got something with the ESD coat Rob. You could market it as "The Process Profesional ESD Smock" (Lead Free smocks available soon). It would be like a regular smock or coat, but have a big "S" on the back like super man. The buttons would be the quick release that Larry or Moon Man could easily unsnap when called the next process emegency!

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Joseph

#40594

Fillet Tearing | 23 March, 2006

Dear all,

Referring comment from Mr. Jack,IPC director certification & assembly technology, the term "fillet tearing" is too broad. Cracks or fractures in the required fillet area, with SnPb or LF alloy and whether you call it tearing or not, is a DEFECT. For lead free alloy in PTH connection "hot tear" that isn't in the required fillet area (next to lead or land) is identified by 610D as Acceptable. Analysis has shown that this tearing affect is nearly always in a copper-rich area of the alloy. Remember that LF solder used for wave soldering is usually about 99.3% Sn and 0.7% Cu. It is hard to keep that very small amount of copper evenly dispersed through the molten tin and sometimes a "clump" of copper molecules will accumulate. Sometimes after processing a lot of PCBs the Cu level in the wave bath increases because of Cu washing or scrubbing from the PCB conductors into the bath. An intermetallic region will form around these Cu molecules and hot tear may occur in between that intermetallic and the copper molecules. As a separate issue, again specific to LF alloys in PTH holes, an anomaly can occur when there are large mass, thick lead through-hole components. Often the preheat process has to be set very high and as a result, these large mass components are much slower to cool down after passing over the wave. The thermal energy in the component and lead means that the thin solder at the edge of the land freezes slower than the solder in next to the lead in the middle of the hole. As it is cooling towards the point it will freeze, it is shrinking in size and the surface tension creates a lot of "pull" stress on the solidified solder on the edges. Depending on all the physics involved, sometimes there is so much stress that the solder pulls away from the copper land around the outside edges. This is called fillet lift. On analysis, it has been determined that this fillet lift always occurs between the intermetallic and the copper land. If there are other conditions that would cause the land to separate, the acceptance criteria is completely different (Chapter 10 of IPC-A-610D). So he mentioned that our customer is correct that 610D has criteria for Hot Tear, but there is no other criteria that would permit acceptance of damage in the required fillet areas, regardless of the type of alloy. He believe the term "fillet tearing" may have meaning only to the person that wrote the Vitronics article but it wasn't used by any of the several hundred members of the 610 or J-STD-001 committees.

So, anybody has any further comment ?

Best regards,

Joseph

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