Hi Stewart,

As I suspected.

Yes PCB substrate is exactly the same (the boards were made to the same 
test spec) as is the substrate on the bottom of the BGA.

Thanks for the advice on micro-sectioning.

Regards,



Administrator wrote:
> Hi Eric,
>
> We have examined many BGA's assembled under both N2 and air. I think
> that any differences would likely be quite subtle. The N2 may help
> quicker wetting and spreading to the PCB substrate, and therefore may
> allow for some flexibility in the reflow profile which is used (perhaps
> a shade lower peak, but aside from IMC growth rates, would have little
> impact on IMC type). 
>
> Have you checked to see whether the PCB substrate is the same in your
> customers application as compared to your tests? The metallisation on
> the PCB can have a surprisingly strong influence over IMC type and
> growth speed at the interface between solder ball and BGA package. What
> is the finish on the device - electrolytic Ni? 
>
> Would suggest that a thorough micro-section analysis is the most
> effective way to define the condition of the materials and learn more.
> Would be a useful benchmarking exercise to compare your test vehicle
> results to customer failure. 
>
> Kind regards,
>
> Stewart
>
> Stewart McCracken
> MCS Ltd.
> Centre House
> Midlothian Innovation Centre
> Roslin
> Midlothian
> EH25 9RE
>  
> m. +44(0)7711 541735 
> t.   +44(0)131 440 9090
> f.   +44(0)131 440 9085
> e.  [log in to unmask]
> w. www.themcsgroup.co.uk
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric CHRISTISON
> Sent: 10 November 2008 10:01
> To: Administrator
> Subject: [TN] Effect of Soldering in a Ni atmosphere on BGA reliabilty
>
> A customer has experienced solder joint failures in a lead free BGA 
> device which are unexpected for us.
>
> The test the solder joints failed was a shock test in the plane of the 
> PWB and the joints failed at the interface between the SJ and our BGA 
> device substrate.
>
> We've done similar tests without failure but when we did our trials we 
> soldered the devices onto the boards in a hot air oven. Our customer 
> used a nitrogen oven. Could this affect SJ strength in any way?
>
> Just wondering whether this is worth investigating.
>
> Regards,
>
>
>   

-- 
Eric Christison Msc
Mechanical Engineer
Consumer & Micro group
Imaging Division

STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom

Tel:	+44 (0)131 336 6165
Fax:	+ 44 (0)131 336 6001

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