Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


CLEANING OXIDIZATION OFF OF WHITE TIN PADS

James

#25200

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 17 July, 2003

COULD SOMEONE PLEASE TELL ME OF A WAY TO CLEAN THE OXIDIZATION OF OF WHITE TIN PADS, I AM GETTING ALOT OF DEWETTING PROBLEMS. AND I CONCLUDED THAT ALL THE BOARDS WITH WHITE TIN ARE HAVING THE SAME PROBLEMS. THANKS FOR THE INPUT.

reply »


RDR

#25205

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 17 July, 2003

The only way I have been able to do it so far is to apply a very agressive flux and then wave the board and then wick all of the pads. (Totaly S#$KS). I trust you will eliminate this finish in the future? I hate tin for this reason.

Russ

reply »

James

#25206

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 17 July, 2003

Any suggestions on trying a paste with a stronger flux?

reply »

#25207

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 17 July, 2003

What is this oxidation? What does it look like?

reply »

James

#25209

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 17 July, 2003

It is really hard to tell what it is. It just looks like parts of the pad did not solder and you can see where the solder would even go around the pad leaving voids.

reply »

#25212

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 17 July, 2003

So, how do you know it's "oxidation"?

If the parts didn't solder, why aren't the parts the problem? Do the parts take-on solder?

Please describe: * Appearance of the post-solder components. * Scope and extent of the problem. * Appearance of the post-solder pads on the board. * Appearance of the pre-solder pads on the board. * Materials used in soldering, type of imm tin solderability protection on your board, and production process, including reflow recipe.

reply »

James

#25228

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 18 July, 2003

The parts adhere solder very well. It does not pertain to a certain part on the board either it is all over the board. I cant really say that it is oxidization all you can tell is that on certain parts of the pad still shows like white tin and that the solder never adhered to it. And on the pads you can tell that they have almost a brownish color to certain areas, some darker than others. I am using Kester 63/37 type R562 and I have the profile to the paste man. spec. It is happening to all of the boards that have white tin. What I have heard in the past is that White tin oxidizes very fast. I am hoping to go to all gold immersion in the future.

reply »

#25229

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 18 July, 2003

If you are saying that you have discolored white tin at in-bound inspection, you have bad boards. The boards are fabricated incorrectly. Your fabricator is deficient.

That is the GREAT thing about imm coatings. You can look at them and determine if there's a problem with the coating. You cannot do that with ENIG. You determine there's a problem with ENIG when you have a pipeline full of partally assembled product. Rework, rework, rework.

Steve Wentz says, "The most common reason for solderability issues with the white tin surface coating during multiple thermal excursions is a thin white tin deposit. Florida Cirtech recommends 0.65 microns, that has proven to be sufficient for at least one year shelf life and up to four passes in assembly. In almost every case I've seen, when the first pass or two solders fine and then problems arise, it is an insufficient thickness of white tin that was on the board."

Our experience is: * Heat cycles deplete the pure tin layer. Each solder cycle reduces the tin thickness by ~0.1 micron (4 uin). So, you may have some minor problems on the second reflow. * You will definitely have issues on the hand soldering - after two reflows you can have copper/tin intermetallic formation * Some immersion tin chemistries only have a 3 month shelf life - others 12 months - you need to know which chemistry you are receiving.

reply »

#25230

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 18 July, 2003

A highly activated flux will begin to corrode the imm tin coating after 10 minutes. Corroded tin has poor solderability.

reply »

James

#25257

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 23 July, 2003

Here we go again. I tried changing paste and that did nothing. Literally solder balled up and flew to the next pad. What would be a short term fix to use up all baards with white tin. Is there a fix if the board house did not manufacturer the boards correctly? Is it too late to fix the problem? We eventually are going to all gold immersion very soon I hope. Thanks for all the input.

reply »

#25258

CLEANING OXIDIZATION OFF OF WHITE TIN PADS | 23 July, 2003

Your fabricator should be able to re-apply the imm tin very easily. Actually, if we had boards like you describe [and we were sure we didn't mess them up], we'd be be making strong implications that our fab would need to make this right.

Don't pin high hopes on ENIG. It's very expensive and creates new problems, like poor solderability and black pad.

reply »

PCB Cleaning

Manufacturing Software