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April 2004

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Subject:
From:
JaMi Smith <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 5 Apr 2004 00:08:01 -0700
Content-Type:
text/plain
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text/plain (143 lines)
David,

You say "The parts I want to replace are BGA CPU sockets (Pentium 4, Socket 478)",
and from this I assume that you are going to have to remove the existing sockets /
parts, which I assume will be done with some sort of hot air removal tool.

It has been my experience that if you use a liberal amount of rosen flux in the
removal process, that you will be left with a small and very uniform amount of
solder on each of the existing pads on the board, and yes, a lot of rosin too, but
the rosin is the key to the process, and it can be cleaned up after the fact.

This is usually just about the right amount of solder to remount the new part,
without having to tough up any of the pads, and without having to clean (solderwick)
all of the existing solder off of the pads and then either re-apply additional
solder paste vial a screen or via some other method.

In other words, if you use a lot of flux, and you are very careful in removing the
old part, what you are left with is just the right amount of solder on the pads to
go ahead and directly install the new part with out doing anything else at all.

Yes, this is tricky, but it is worth a try to see if you can remove the old parts
and leave just enough solder behind, and yes the flux is messy also, but after you
remove the old part and inspect the pads, if you are not happy, and do not think
that it will work, then you can go ahead and clean (solderwick) off all the excess
solder from the pads and go about trying some of the other suggestions to place the
new part, and you will have lost nothing.

JaMi Smith


----- Original Message -----
From: "David Tremmel" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, April 02, 2004 11:35 AM
Subject: Re: [TN] BGA socket placement


> Mr. Gregory,
>
> I would like to use a pre-formed tab to minimize labor costs and to
> compensate for the 'lack of dexterity' the people who will actually be doing
> the rework have (or don't have).
>
> As far as 'wanting to add extra volume to the spheres' I think that I lack
> the eloquence (or technical wordage) to put it differently ;)
>
> The parts I want to replace are BGA CPU sockets (Pentium 4, Socket 478)
> which have SMD capacitors soldered to the PCB, in the center area of the
> socket.  A preformed tab, if such a beast exists, would save us the
> time/cost of removing/replacement the components to avoid stencil co
> planarity issues.
>
> Thank you for your response.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
> Sent: Friday, April 02, 2004 12:18 PM
> To: [log in to unmask]
> Subject: Re: [TN] BGA socket placement
>
> Hi David!
>
> Not sure quite you mean when you say; "Pre-formed tab to add extra volume to
> the spheres." Can you elaborate further?
>
> You also say that you want to avoid adding solder paste, can I ask why? If
> the ball-pitch, ball count, and ball pattern is pretty standard, you can buy
> 10
> Flextac stencils from Circuit Technonolgy Center for around $50. They work
> wonderfully too! Go to:
>
> http://www.circuittechctr.com/products/201-3120.shtml
>
> and check them out. I've got pictures up on my page of me using one to
> solder
> a Power PC BGA to a SMT-to-PTH adapter, which I'm sure if there wasn't
> something like Flextac stencils around, would have been a real bear to do.
>
> Give us a few more details...
>
> -Steve Gregory-
>
>
> > Hello Technetters,
> >
> > I have some BGA sockets which I am trying to solder to PCBs.
> >
> > The sockets have stand-offs which prevent the solder spheres from
> collapsing
> > and making a good mechanical/electrical connection.
> >
> > Ideally what I am looking for is a pre-formed tab to add extra volume to
> the
> > spheres.  I do not have an in-house machine shop to make a stencil to
> apply
> > paste and quite frankly I would like to avoid that course if possible.
> >
> > Thank you in advance for your help,
> >
> > David Tremmel
> > Technical Manager
> > Belmont Component Services
> >
>
>
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