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Solder wetting issues

Views: 1733

Amol Kane

#38168

Solder wetting issues | 1 December, 2005

Hi, I am having a SAC 305 solder paste with water soluble flux wetting issue. during reflow, the solder melts, but doesnt flow. the reflow profile was developed by the solder company person (Kester). the board is a test assembly to validate our LF process. Surface Finish is Immersion Sn

the picture is at the following link

http://img232.imageshack.us/img232/2126/sn017qfp208visual6oj.jpg

the solder has reflowed because i can see voids under the X-ray......Any Thoughts??

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Bill C

#38169

Solder wetting issues | 1 December, 2005

It looks to me that your reflow profile is not hot enough. Seeing the granular structure of the solder paste still on the board would indicate the paste has not reflowed entirely.

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Amol Kane

#38170

Solder wetting issues | 1 December, 2005

my first thought was that too, but all the other components on tha board have reflowed properly. I have tow test boards, one with Imm Sn and other with Imm AG. on both these boards only the QFP has this solder phenemenon

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URL

#38172

Solder wetting issues | 1 December, 2005

You need to verify if you're getting up to the needed temps. It looks like you're not. I'd say it started to reflow but never reached a long enough time. Nitrogen may help with further wetting.

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#38175

Solder wetting issues | 1 December, 2005

Are you sure you're getting enough paste on the pads? It looks like you may not have enough flux to get the solder to wet properly.

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RDR

#38176

Solder wetting issues | 1 December, 2005

Your paste is oxidizing in reflow and not coelescing (spelling?) We failed kester W.S. for reasons such as this. There NoClean is a little better but we do not use that either. I would switch pastes and I will bet that your problem majically disappears.

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#38180

Solder wetting issues | 1 December, 2005

Does the solder melt when 'hit' with a soldering iron [and maybe a little flux]? If so, what is the appearance of the solder flow?

What causes the green tint in the picture you provided?

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Amol Kane

#38184

Solder wetting issues | 2 December, 2005

Davef and russ, thank you for your input

The kester was selected due to a management decision, I shall recommend that other solder be tried out as well.

davef, i'll try out the soldering iron......and also look for the green tint (didnt notice that before....might be the camera)

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#38185

Solder wetting issues | 2 December, 2005

Good evening,

I�ve just solved very similar soldering issue. In my case the problem was with 0603 chips. Solder joint had same appearance. I suspected that solder do not melted and increased TAL and peak temperature. No result. Next thing I tried to do is to reduce preheat ramp and increase soak time. Solder started to melt properly. My conclusion is that flux burned too fast and I tried to reflow lead oxide. When I �hit� defective joint with soldering iron solder doesn�t melt. Am I right?

Thank you.

BR, Pavel

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RDR

#38186

Solder wetting issues | 2 December, 2005

You hit it on the nose Pavel, the fluxes in paste are formulated to have 2 activating points if you will, one at low temp and one at high temp. when the low temp flux gets killed this is what you will see. This is the main reason we opted out of Kester. Other Mfgrs. are much more forgiving with different types of profiles.

Russ

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#38265

Solder wetting issues | 7 December, 2005

I'm curious to know, if using the same paste and profile,would this phenomena would occur on Copper OSP boards...any input?

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Samir Nagaheenanajar

#38275

Solder wetting issues | 7 December, 2005

Here in Rihad, I am in the midst of Pb-Free implementation, and most of our paste manufacturers have advised that with the higher peak temperatures, you need to retain the activators as long as possible. I have changed our profiles to a more gradual ramp rate (ramp to 150 for about 2 min.) and also ensure that I soak at 150C-170C(a light knee, but not a flat soak) for about 45 - 60 seconds, and then spike up to liquidous & peak...

The other guy was right about Kester. At my last company, our management was getting kick-backs from Kester, and we were forced to use it, and even Kester's Lead-Paste profiles had a very unforgiving process window.

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