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browny, brassy, dark, HAL Pb-free pads

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#72131

browny, brassy, dark, HAL Pb-free pads | 20 May, 2014

Hi, I am facing an issue with PB-free HAL on our boards (270 pcs of 800pcs lot). I look for a root couse for this issue and I guess it is strongly related with PCB manufacturing process.

In attachment you can see PCB with dark pads. They turned grey/dark color after 1 pass through reflow with max peak temp. 250C

I've searched smtnet forum but could not find any topic which explains where is the problem . Could you please help me finding root couse ?

Regards, Andrzej

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#72132

browny, brassy, dark, HAL Pb-free pads | 20 May, 2014

From the picture I would say the problem lies with the PWB manufacturer. It looks as though some part of the plating process was not optimal during the PWB production run, and you have the resulting discoloration following the reflow process.

What is scary is that the portions of the assembly that appear to have soldered well, only MIGHT HAVE soldered well. You might have this same condition at all pad locations to a lesser degree, to a point where the solder is still wetting somewhat, but also to the point that there may be compromised solder joints that you cannot see.

Definitely a process indicator for the PWB fabrication, I would think. Might want to have the board house out for a look at their product right off the bat...

Good Luck 'hege

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#72140

browny, brassy, dark, HAL Pb-free pads | 23 May, 2014

Thanks Hege.

I've done some research and this might be the root couse:

1. Too thin HAL layer which leads to formation intermetallic Cu-Sn layers on surface after 1-st reflow (most probably)

2. Poor quality of solder for HAL process.

3. Problem with cleaning – maybe post clean line water not clean and not fresh water soluble flux

4. Conditions of stocking in factory are not optimal or factory stock them longer then expected shelf life which leads to formation of "tarnish" or other problems on the pads surface

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#72145

browny, brassy, dark, HAL Pb-free pads | 23 May, 2014

You are on the right track for sure Andrzej. Conditions 1 and 4 I see often enough, but I would also lean towards condition 1, like you. 'hege

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