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Subject:
From:
Tegehall Per-Erik <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 13 Oct 2003 14:44:46 +0200
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Jim,

I noted when I went through my emails that nobody answered your question. In this discussion only ENIG on PCBs has been discussed but, as you pointed out, you can have ENIG also on the solder lands on the BGA. That is perhaps even more dangerous since that interface will go through at least two soldering processes (the first when the ball is attached to the solder land). Therefore, the intermetallic layer will be thicker there. In fact, most brittle fractures we have seen that has not been related to "black pad" have occured towards the solder lands on the component and not towards the solder lands on the PCB. Thus, stop using ENIG on the PCB will not eliminate the risk for brittle fractures. 

It is also common to have electrolytic nickel/electrolytis gold on the component solder lands. The gold layer then may have a thickness of 1.0-1.5 um. Then you may have a new form of gold embrittlement due to a formation of a NiAuSn-IMC layer on top of the NiSn-IMC layer after some time that depends on the temperature. This occurs at gold concentrations as low as 0.3 %. This was discussed some time ago on TechNet.

Per-Erik Tegehall
IVF, Sweden

-----Ursprungligt meddelande-----
Från: Marsico, James [mailto:[log in to unmask]]
Skickat: den 7 oktober 2003 13:59
Till: 'TechNet E-Mail Forum.'; Tegehall Per-Erik
Ämne: RE: [TN] ENIG solder joint embrittlement


This is interesting...  is anyone addressing the ENIG sometimes used on the
BGA component prior to ball attachment?

Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]> 
631-595-5879


        -----Original Message-----
        From:   Tegehall Per-Erik [SMTP:[log in to unmask]]
        Sent:   Tuesday, October 07, 2003 3:02 AM
        To:     [log in to unmask]
        Subject:        Re: [TN] ENIG solder joint embrittlement

        Eddie,

        As David already has pointed out, it is soldering to a nickel
surface that is the issue, the gold layer is too thin to cause gold
embrittlement. Below are two quotations from a draft of IPC-7095A, "Design
and Assembly Process Implementation for BGAs", supporting that solder joint
embrittlement is indeed an issue when ENIG is used.

        "Recent preliminary analysis indicates that the BGA brittle solder
joint fracture happens under a high level of both applied strain and strain
rate even if hyperactive corrosion (i.e. "black pad") does not take place".

        "Based on industry experience over the past several years, it
appears that BGAs and nickel surface coatings may not be an ideal
combination. If nickel surface coatings are used with BGAs it is recommended
that the BGA surface area not exceed 25 mm2."

        Per-Erik Tegehall
        IVF
        Sweden

        -----Ursprungligt meddelande-----
        Från: Eddie Rocha [mailto:[log in to unmask]]
        Skickat: den 6 oktober 2003 23:51
        Till: [log in to unmask]
        Ämne: [TN] ENIG solder joint embrittlement


        Does anybody have data or literature which shows that solder joint
        embrittlement is not an issue when ENIG is used? I have a customer
        that needs this supporting data before he can allow us to use ENIG.
Is
        this embrittlement issue related only to a certain thickness of
gold?
        I'd appreciate any feedback on this topic.
        thanks,

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