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November 1998

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Subject:
From:
"Wolfe, Robert" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 16 Nov 1998 11:46:04 -0500
Content-Type:
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text/plain (88 lines)
Khaled asked why neckdown.
Just meaning that if you are trying to connect a massive trace like .3 .4 or
.5 wide to a .062 pad on a chip (thereby having solid copper all around the
pad), (I realize a trace of this size would not be able to connect to center
of pad without shorting to the one next to it, but my point is that if there
is solid copper on at least 3 sides of the pad) and you want to have a good
solder joint,  you may want to provide some thermal relief either by
creating a positive thermal connection to the pad if cad software will do
this or necking down the trace close to the pad to kind-of create a thermal
relief for the pad. Hope this was clear enough just in words.
Robert M. Wolfe

        -----Original Message-----
        From:   Khaled H. Fouad [SMTP:[log in to unmask]]
        Sent:   Thursday, November 12, 1998 6:35 PM
        To:     [log in to unmask]
        Subject:        Re: [TN] neckdown

        "Wolfe, Robert" wrote:
        >
        > Neckdown is a term used when a trace needs to be less wide in an
area to get
        > through pad/lands or just for pad entry because of solderability
issues.
        > I.E. say a conductor trace on a board is being routed at .025 wide
and you
        > need to get between two pads that have a .020 clearance between
them you
        > will need to neckdown the trace to say .008 wide. Or you are
entering a .062
        > pad with .10 trace and need to neckdown to say .040 close to the
pad for
        > solderability. Longwinded but basically making a trace less wide
for a short
        > distance to maintain design rule clearance or solderability.
        > Robert M. Wolfe
        >
        Hi Robert
        Why do you need to neckdown a trace when you enter a pad. Is this a
DFA
        vaiolation,plz explain ?
        --
        Best Regards
        Khaled H. Fouad

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