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lead free joint finish

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#57895

lead free joint finish | 28 January, 2009

Hello! I am having trouble with the new changes from lead joint to lead free joint, we are working on change to lead free, I am using a 3 zone oven reflow, the zone temps are :

zone 1 zone 2 zone 3 (top and bottom) 128 208 260 the conveyor it has a speed of 0.55m/min

the thing is that when we look at it under microscope it looks like it has little balls and some look rugged.

it should look like that? or I have a problem with the profile in my oven?

where can I see a good solder joint finish for lead free ?

I really appreciate all you input thanks

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#57896

lead free joint finish | 29 January, 2009

Hi Armando,

I think you have to buy a bigger reflow let say 7 zones to get the correct profile. The reason you are getting that problem is due to short profile time.

What is the size of your board? What is the composition of your solder paste? Please let me know also your profile peak temp? I think your peak temp will be very low.

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#57897

lead free joint finish | 29 January, 2009

There are two profiles available for the Pb-free process: (1) RSS and (2) RTS. In your case, you should try a solder paste that supports RTS profiles. A minimum of 7 zone Refow Oven would be fine on the Pb-free process. However, you may still try by analysing your parameters. What is the length of each zone? What is the cooling mechanism used by your Oven / how many cooling zones used? Ensure to spend as much time as possible to arrive at the optimum profile. Above all, a Pb-free joint cannot match the cosmetic result as seen on a eutectic Sn-Pb joint.

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#57901

lead free joint finish | 29 January, 2009

As others have said, you'll have some difficulties getting good reflow on pb-free out of a 3-zone oven. We did it with a 4-zone for awhile, but only had really good success on low thermal density boards.

That said, you should definitely check your time above liquidous. We suspect that in the length of time that your board is in the oven, it's not above the recommended TAL for long enough. We're also generally concerned about the ramp rate in such a small oven; you stand a chance of thermally shocking the parts on the board.

cheers ..rob

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#57906

lead free joint finish | 29 January, 2009

Hi Small ovens work fine if the settings are correct and I seriously doubt 55cm/min is right. Profile it and speed down to around 35cm/min. Increase first zone to around 170 keep second at 208 but increase last to around 280 BUT profile to check it out FIRST. What reflow oven are you using I maybe able to ask on eof my guys to see if they have settings saved for it to get you a start point Cheers Greg

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#57909

lead free joint finish | 29 January, 2009

HI!!!

its a ERSA Reflow Oven HotFLOW 7

and I really appreciate some help thanks

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#57914

lead free joint finish | 30 January, 2009

Hi Armando

Hotflow 7 is a big machine and one of the best Reflow ovens around (in my opinion), well suited for Lead Free. A typical 1.6mm board has the following settings for Lead Free SAC305 paste

All Temperature settings are Top and Bottom Preheats:

1.190C 2.180C 3.275C

Conveyor Speed for this BIG oven is the same 55cm/min.

These settings are from a working customer using our Lead Free Paste and get very good results. Obviously if the board is densely populated or ground planed up then you may need to tweek a little but these should give you a good starting point

All the best Greg York

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#57927

lead free joint finish | 2 February, 2009

Everyone's telling you setpoints, but yet, we haven't seen a thermal profile from you. It'd help if you can provide this, and using everyone's recommended setpoints, determine if your profile is meeting:

1.)Time Above Liquidus

2.) Peak

3.) Ramp Rate

1 & 2 are key for successful reflow.

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