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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Alternate surface finishes

#10943

Alternate surface finishes | 18 June, 1999

We currently use HASL on all of our boards and I would like to move to something else. I have sampled some boards with Entek OSP and I loved it, the problem is we have plated mounting holes on just about every board we make. Does anyone have information on how the exposed copper will react over time? I know it will oxidize, but how badly? I have also considered a two step process with OSP on the pads and gold on the mounting holes, is this feasable?

I have also sampled some boards with gold flash and was not impressed with the thru-hole wicking. Any experience with Palladium finishes? All help is appreciated.

James

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Earl Moon

#10944

Re: Alternate surface finishes | 18 June, 1999

| We currently use HASL on all of our boards and I would like to move to something else. I have sampled some boards with Entek OSP and I loved it, the problem is we have plated mounting holes on just about every board we make. Does anyone have information on how the exposed copper will react over time? I know it will oxidize, but how badly? I have also considered a two step process with OSP on the pads and gold on the mounting holes, is this feasable? | | I have also sampled some boards with gold flash and was not impressed with the thru-hole wicking. Any experience with Palladium finishes? All help is appreciated. | | James | | We currently are using OSP/OCC for a wide variety of board types including those with the same mounting requirements as you. Though oxidation always is a problem with bare copper, those pads covered, and secured, with mounting hardware pose little problem except discoloration. If you save and like pennies, you'll like the look of oxidized bare copper.

Using differential plating, to cover only mounting holes/pads, is an expensive proposition. You may try solder mask as an alternative provided it meets all your other requirements.

One issue I might bring up is that of minimizing mis-printing and washing panels after. There are very strict guidelines for cleaning OCC/OSP with temperatures not exceeding 140 degrees F. with pressure not exceeding 40 psi and you only have one real opportunity.

I've used flash gold successfully and liked it. However, it is an application critical process, as are most, depending on careful supplier process management. I've only worked with two board shops successfully. One is Praegitzer. The other is Multek.

I must caution industry still is concerned about nickel barrier intermetallic formations and the apparent deleterious effects it has on solder joint reliability. Check Motorola for more details.

Palladium has its own set of problems. I've not used it in the PCB world but have experience with it in the hybrid thick film arean. Again, Praegitzer is touting this surface finish as one to watch.

Electroless silver had promise, from Alpha, but I don't know where this ended up. Also Omikron's "white" electroless tin is proported to be a good alternative, though I've never been a big fan of tin in any application.

Earl Moon

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#10945

Re: Why not Tin | 18 June, 1999

What's wrong with the Tin? Just wondering

MDCox | | Electroless silver had promise, from Alpha, but I don't know where this ended up. Also Omikron's "white" electroless tin is proported to be a good alternative, though I've never been a big fan of tin in any application. | | Earl Moon |

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Earl Moon

#10946

Re: Why not Tin | 18 June, 1999

| What's wrong with the Tin? Just wondering | | MDCox | | | | Electroless silver had promise, from Alpha, but I don't know where this ended up. Also Omikron's "white" electroless tin is proported to be a good alternative, though I've never been a big fan of tin in any application. | | | | Earl Moon | | | | Tin is a metal that's surface oxidizes almost as quickly as copper. Oxidation is real problem, as you know, and a barrier to solder wetting. However, I have little experience with what makes "white tin" better than its grey cousin. I am sure the kind folks who supply the process will provide imperical evidence that it works. Some others think so.

Earl Moon

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