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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Immersion Gold

Chris May

#9231

Immersion Gold | 30 September, 1999

I am having problems processing immersion gold boards. The achieved solder joints appear acceptable a la IPC-A-610, but the resultant joint does not fully cover the land, i.e. you can still see an outline of gold pad. What is the best way to achieve a "better" joint on gold ????

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#9232

Re: Immersion Gold | 30 September, 1999

| I am having problems processing immersion gold boards. The achieved solder joints appear acceptable a la IPC-A-610, but the resultant joint does not fully cover the land, i.e. you can still see an outline of gold pad. | What is the best way to achieve a "better" joint on gold ???? | Same thing happened to me last week. The subcon admitted that there was a problem in paste printing. According to IPC there was nothing to say against the joints but for safety reasons they had one board examined at an independend institute with the result that everything according to the solder connection was ok and a shear test also showed normal results so rework is not necessary and not recommended for cosmetic purposes only. Knowing that and one pcb poorer but gained 99 boards they lived happily ever after and hope that this will never happen again. Normally the look of the joints and the wetting with no-clean under correct treatment are no matter of complaint.

Give it a test

Wolfgang

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#9233

Re: Immersion Gold | 30 September, 1999

| | I am having problems processing immersion gold boards. The achieved solder joints appear acceptable a la IPC-A-610, but the resultant joint does not fully cover the land, i.e. you can still see an outline of gold pad. | | What is the best way to achieve a "better" joint on gold ???? | | | Same thing happened to me last week. The subcon admitted that there was a problem in paste printing. | According to IPC there was nothing to say against the joints but for safety reasons they had one board examined at an independend institute with the result that everything according to the solder connection was ok and a shear test also showed normal results so rework is not necessary and not recommended for cosmetic purposes only. | Knowing that and one pcb poorer but gained 99 boards they lived happily ever after and hope that this will never happen again. | Normally the look of the joints and the wetting with no-clean under correct treatment are no matter of complaint. | | Give it a test | | Wolfgang | Wolfgang: I agree that this appears to be a cosmetic problem, but what kind of "paste printing" problem did your supplier have? What kind of print problem would prevent the paste from wetting the edges of the pad? Sounds screwy to me!!!! Now, solder mask bleed onto the pads that's more believable. My 2�. Dave F

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Brian

#9234

Re: Immersion Gold | 1 October, 1999

| I am having problems processing immersion gold boards. The achieved solder joints appear acceptable a la IPC-A-610, but the resultant joint does not fully cover the land, i.e. you can still see an outline of gold pad. | What is the best way to achieve a "better" joint on gold ???? |

As has often been pointed out, immersion chemistry is hairy. Immersion gold is porous and has organics co-deposited which will eliminate much hope of a decent solder flow, even assuming the underlying nickel has not oxidised, which is all too common. IMHO, this finish is more cosmetically appealing than technically desirable (and VERY profitable for the PCB maker). Your experience is very common and wetting balance tests on this finish often give horrendous results.

IF the problem is more with the nickel underplate (or copper) being oxidised through the porous gold, then using a good, strong, water-soluble paste should achieve wetting. IF the problem is due to the gudge which goes on with the gold, then there is little that can be done to improve the situation.

Sorry, I know this isn't helpful, but it's the best I can say.

Brian

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#9235

Re: Immersion Gold | 1 October, 1999

| | | I am having problems processing immersion gold boards. The achieved solder joints appear acceptable a la IPC-A-610, but the resultant joint does not fully cover the land, i.e. you can still see an outline of gold pad. | | | What is the best way to achieve a "better" joint on gold ???? | | | | | Same thing happened to me last week. The subcon admitted that there was a problem in paste printing. | | According to IPC there was nothing to say against the joints but for safety reasons they had one board examined at an independend institute with the result that everything according to the solder connection was ok and a shear test also showed normal results so rework is not necessary and not recommended for cosmetic purposes only. | | Knowing that and one pcb poorer but gained 99 boards they lived happily ever after and hope that this will never happen again. | | Normally the look of the joints and the wetting with no-clean under correct treatment are no matter of complaint. | | | | Give it a test | | | | Wolfgang | | | Wolfgang: I agree that this appears to be a cosmetic problem, but what kind of "paste printing" problem did your supplier have? What kind of print problem would prevent the paste from wetting the edges of the pad? Sounds screwy to me!!!! Now, solder mask bleed onto the pads that's more believable. My 2�. Dave F | Hi Dave, as stated by the subcon they normally perform AOI after printing. In this particular case the nightshift (they might have done that also before) turned AOI off for speed purposes and the amount of paste wasn�t checked at all so in some cases their wasn�t enough paste due to whatever they let go so in some (many) cases a full wetting of the whole pad wasn�t achived. They did rework the worst cases but send the units without further notice. My first concern was that something was wrong either with Ni/Au plating or contamination of the lands so I had that checked and that�s what I would suggest in similar cases where optical inspection alone can�t answer all your questions and doubts. Details and the report will be discussed in about 10 days and until than there will be no final OK for the boards.

So for the bad wetting there could be more causes, contamination, storage problems, bad paste, inadequate handling, printing, maybe profiling etc. To decide where to put your focus on you will have to know the particular cause to change or improve processes.

Can�t say what�s most probable in each case, it was just my latest experience Wolfgang

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