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Palladium poor wetting

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Steve

#41714

Palladium poor wetting | 22 May, 2006

I have read some threads about poor wetting on palladium-silver (Pd-Ag) coated components. I followed the suggestions, but I am still having a problem.

The part is an 0603 chip type (Vishay varistor). The Process: solder paste is lead-free Alpha Metals OM-338, reflow peak is ~235�C, time above 221�C ~55s. After reflow it looks like there is no solder on the pads, like the part wicked up all of the solder. I have seen these before where the part is sitting on a pillow of solder, but this is different.

If we manually add solder to the pads after screen print, the part wets fine. But we can't be adding solder to every Pd-Ag component. Any suggestions?

Thanks, Steve

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Loco

#41716

Palladium poor wetting | 23 May, 2006

No suggestions, but we've also had problems with silver palladium. No wetting on reflow, when we tried handsoldering them, we could actually scrape off the whole finish and were left with a black unsolderable underground. It was just 1 reel, seems the manufacturer changes the finish on newer ones (although we ordered silver palladium). So problem solved itself this time.

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RDR

#41719

Palladium poor wetting | 23 May, 2006

Seems as though the problem is with PCB and not component? "Solder does not wet to pads, wets to component"

What is your board finish?

Russ

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Steve

#41720

Palladium poor wetting | 23 May, 2006

Had exactly the same type of issues. Tried everything from pre fluxing the pcb's , various ammendements to the oven profile and various pastes.

Finally after a lot of help from multicore we settled on a paste by the code of cr39. A no clean flux with a more active flux. May I also recommend Tamura as a alternative this paste is second to none.

Good luck.

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Steve

#41723

Palladium poor wetting | 23 May, 2006

Sorry I misled you. The PCB pads are wetting, but there is no fillet being formed. After reflow, it looks as though no paste was put down on the pads; however the paste print is fine. All other components solder real nice, it's only the Pd-Ag parts that won't solder.

Steve

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Steve

#41724

Palladium poor wetting | 23 May, 2006

Not being funny here but I understand exactly what you are saying and sounds exactly the same as we experienced.

Seriously try a different paste. Give Tamura a ring and I am sure they will give you a sample. I don't have the exact part code but they only manufacture the one lead free type.

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#41725

Palladium poor wetting | 23 May, 2006

They work well in silver conductive epoxy in hybrid applications. They are very poor in no clean applications. They don't work that well in OA solder paste either. Used them once in OA paste and in a nitrogen. They looked just fine. Solder to Pd/Ag termination failed under shock and vibration. You are better off finding another part or different type termination material.

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#41743

Palladium poor wetting | 23 May, 2006

First, where the temperatures that aare mentioned in the original post measured?

Second, it sounds like the PdAg component terminations are not seeing enough heat [your soldering iron touch-up proves this]. Your 232*C peak is the absolute minimum suggested in Alpha Metals' data sheet. You should be tayloring your reflow recipe for the PdAg component, not the other very nice components. Crank-it-UP!!!

Third, your TAL of 55 sec is no where near the top of the range [TAL 35-90 sec] suggested by Alpha Metals. Consider a longer time, because Pd and Ag both increase the liquidus of your SAC alloy.

From Alpha Metals OM-338 data sheet: ATMOSPHERE: Clean-dry air or nitrogen atmosphere. PROFILE (SAC Alloys): A straight ramp profile @ 0.8�C to 1.7oC per second ramp rate is recommended (TAL 35-90 sec and peak 232-250oC). (1) Higher density assemblies may require preheating within the profile and may be accomplished as follows: - From 40�C to Liquidus: Between 2min 30 sec. and 4 min. (optimum(2) is 3 min.) - From 170�C to Liquidus: Between 45 sec. and 75 sec. (optimum(2) is 1 min.) - From 130�C to Liquidus: Between 1min. 20 sec. and 2 min. 15 sec. (optimum(2) is 1min. 30 sec.) - Time above liquidus: Between 30 sec. and 90 sec. (optimum(2) is 45 sec. to 70 sec.) Note 1: Refer to component and board supplier data for thermal properties at elevated temperatures. Lower peak temperatures require longer TAL for improved joint cosmetics. Note 2: OM-338 is designed to work under a wide range of reflow profiles in order to find the optimum profile for your process. This can be achieved by balancing: (1) Minimum Delta T�s (depending on board mass and thermal oven characteristics) (2) Maximum Reflow Yield (includes voiding, cosmetics, solder balling, etc.) (3) Minimum Stress and Overheat for Components and Boards (refer to suppliers� guidelines and specifications. Contact your local Cookson Electronics Application Engineer for further details.

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Steve

#41762

Palladium poor wetting | 24 May, 2006

The temperatures were measured on the board, ~1/2" away from the components in question.

Admittedly the profile is on the bottom end of the Alpha recommendations. The profile was set up this way intentionally to avoid heat damage to other components. I obviously need to re-evaluate this since we will be seeing more and more Pd plated parts.

Thanks for the input.

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#41772

Palladium poor wetting | 25 May, 2006

Hi I manufacture ceramic parts that have a terminations that are palladium/platinum/silver or any combination of the 3.

Termination Ink usually consists of 3 main parts the alloy, glass frit and binder. Binder is to help bind everything together while still wet , glass frit is there to bond the alloy to the ceramic substrate and the alloy is present to give a solderable finish. if the ink is fired at a temperature that is too hot the glass frit can be dispersed through the metal content, also if firing occurs more than once the glass frit can work its way to the surface of the termination. this usually creates two problems 1 the termination isnt bonded to the ceramic so leaching of the temination occurs more readily 2 as the glass frit is on the surface wetting is a big problem. which is what i think your seeing.

Normally if we have this problem we scrap the parts as you cant rework them.

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#41774

Palladium poor wetting | 25 May, 2006

The warmest spot you measure on the board is the bare laminate. It will be 10*C hotter than a solder connection.

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#41779

Palladium poor wetting | 25 May, 2006

Had the same problem with a batch of 0603`s nfrom Vishay. They eventually replaced the components after I proved that the problem was with the component.

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#41780

Palladium poor wetting | 25 May, 2006

Print a number of pads of the 0603 on to a ceramic substrate. Then place the 0603 on the paste on the ceramic and refow. If the paste shows no wetting onto the component it will prove that there is a problem with the components solderability.

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