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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Poor reflow over gold plating

We are experiencing a situation that we would really appreci... - Jun 28, 2005 by

Add this forum to your site! Click to learn more. SMTA

Matt Kehoe

#35198

Poor reflow over gold plating | 28 June, 2005

We are experiencing a situation that we would really appreciate some expert opinions on. Our process prints solder paste then reflows it without components. Normally the paste wicks into a very shiny rounded meniscus. Even over gold, the round pads are predictable and repeatable although not as shiny as the HASL version.

We ran 8 of 22 boards yesterday through our normal print and reflow process and ended up with solder that was dull, grainy, and from what we could tell, not completely reflowed. See pics at http://www.sipad.net/SSi_QA/Gold_reflow2.htm

Some initial opinions have to do with too much gold plating on the pads. We ran a few HASL boards with the same paste, same profile etc, and they looked perfect.

Any ideas?

Matt Kehoe mkehoe@sipad.com

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »


RDR

#35199

Poor reflow over gold plating | 28 June, 2005

It appears that the reflow profile was incorrect or the paste was in bad shape on these boards from what I can see. I personally have never seen a board finish cause this symptom.

reply »

#35200

Poor reflow over gold plating | 28 June, 2005

Points to consider are: * Gold plating too thick [SB LT 8 uinches]. [Obviously, we're talking about actual plating thickness, not the specification.] * Reflow recipe improper [SB 220*C 5-10 sec]. A recipe that works fine for HASL needs to be hotter when soldering gold. Different alloy, different recipe.

reply »

GS

#35202

Poor reflow over gold plating | 28 June, 2005

I am not an expert but just for my understanding:

- solder paste used ? NC ? other ? - reflow in Air or N2 ? - temp ramp up before soack (�C/second) ?

Tnks

GS

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »

#35203

Poor reflow over gold plating | 28 June, 2005

Thanks for the replies,

- solder paste used ? NC ? other ? Water soluble 63/37 paste

- reflow in Air or N2 ? Infrared

- temp ramp up before soack (�C/second) ? Will have to check.

This profile has been used on numerous gold plated boards in our shop with not problems. We are reflowing without components, bare boards, so the profile is usually the same for all our boards as long as the thickness and solder paste specs are the same.

We ran a HASL job this morning with the paste from yesterday and the pads are perfect, shiny, and bright.

Frustrating to say the least.

mk

reply »

#35207

Poor reflow over gold plating | 28 June, 2005

Matt, Try a cooler profile by simply speeding up the conveyor by 10%. The difference may be the temperature the pads are reaching between the HASL boards and the Au boards. Are they the same thickness?

reply »

#35209

Poor reflow over gold plating | 28 June, 2005

Yes, .062 fr4. Like I said before, we run a lot of gold boards, as many as 25% of what goes through the shop, and we've never adjusted anything before??? Many of these are bigger by 2 X and much more dense. Reflow is not as shiny as HASL but always uniform and smooth.

Hypothetically, if the gold were on there really heavy, could that make the paste do what the pictures show?

Is there a way to check the thickness of the gold. Isn't there a machine called a Caviderm or something like that, that can measure the gold thickness?

I just don't want to mess with any more of these unless I am sure of good results. Matt Kehoe SIPAD Systems Inc. 360-C Winkler Drive Alpharetta, GA. 30004 www.sipad.com mkehoe@sipad.net 770-475-4576 770-475-1597 fax 404-680-7977 cell SMTA Member

reply »

#35210

Poor reflow over gold plating | 28 June, 2005

We got the same problem. To solve it, we have to tint the pads first and do the normal reflow process. It works but take a lot of time to tint the pads.

Any thoughts? Thanks, -Michael

reply »


RDR

#35211

Poor reflow over gold plating | 28 June, 2005

Matt, have you run a profile on this board? Just because it's .062" doesn't mean that any old .062" profile will work. We have .062" thick boards that almost nil for copper and other are utilizing 2 oz. layers internally. They require quite different profiles.

I am curious if anyone has seen thick gold do this or are these pads contaminated someway? I have ran very thick gold in the past (plated as in like a gold finger thickness)and never saw any visual signs that anything was wrong but the boards did fail for fractured joints from embrittlement.

It may be only me but in looking at these pictures they just flat out appear that the reflow cycle was inadequate or the paste oxidized severely in the oven during the heating stages.

I suppose that there is no chance that these boards went through the oven before it was ready?

reply »

Bob Gilbert

#35212

Poor reflow over gold plating | 28 June, 2005

Matt, Try putting a soldering iron to a pad to see if you get reflow. If it reflows, your oven is too cool. If no reflow, your oven may be too hot. Regards, Bob

reply »

#35214

Poor reflow over gold plating | 28 June, 2005

Matt: Yes, if the gold was really thick, it could appear like your pictures.

In measuring gold plating thickness, we'd want to use xray fluorescence [XRF]. For alternatives, look here: http://www.pfonline.com/articles/pfd0027.html

reply »

#35215

Poor reflow over gold plating | 28 June, 2005

Michael: What's this "tint"? How do you do it? Tell us more, please.

reply »

#35220

Poor reflow over gold plating | 29 June, 2005

Hi Bob,

We tried flowing the pads with a soldering iron. The pad at the tip of the iron went shiny but as soon as the iron was taken away, the pad returned to the dull finish. You could actually move the tip around the pad and it would shine up then go back to dull black as soon as the iron was moved off. Same with the fine pitch.

mk

reply »

#35228

Poor reflow over gold plating | 29 June, 2005

When discussing this with the customer he said that his vendor recommended a hard gold plating finish on the board due to the BGA.

I said "hard gold"??? And he said yes, hard gold.

Turns out the boards were plated with hard gold, not ENIG.

Thanks for all the help.

reply »

GS*

#35231

Poor reflow over gold plating | 29 June, 2005

Very interesting tread, many thanks to all.

Matt please, now what does it mean for you? Will your custmer accept dull solder joints or will the plating be changed ? (ie. HASL, ENIG, etc)

Tnks and regards

GS*

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »


RDR

#35239

Poor reflow over gold plating | 29 June, 2005

I guess it's it's a good thing that they didn't work out. It might have been interesting when all of the boards failed down the road. I knew I should have asked if it was enig instead of assuming that it was.

reply »

#35261

Poor reflow over gold plating | 30 June, 2005

Matt: What thickness of hard gold was applied to your customer's boards?

reply »

Mason Hughes

#35262

Poor reflow over gold plating | 30 June, 2005

Hi, In response to reading height or gold thickness, I can do that <= one micron if that helps. It will read the thickness of the gold given the local reference plane is accurate and I have a shot at the copper or other under layer as an accurate reference plane. you can send me a pcb and will run the test if you like. or you can do yourself on machine. masonhughes@sbcglobal.net

reply »

#35380

Poor reflow over gold plating | 8 July, 2005

I did not get that info. We sent them back and the vendor ran them through HASL finish. They processed very well after that.

Thanks to everyone for the help.

mk

reply »

IMRANH

#35415

Poor reflow over gold plating | 10 July, 2005

HI I am IMRAN i am not expart for it but i tell you one thing you cheak your PCB in microscompe may bee posibal you can see veary thin lear on the pcb pad. its come from pcb monufacturer whan they pass form chmical solution its lear may bee com. pl chak that thank you

reply »

Reflow Oven

reflow oven profiler