BGA fix needed

[Boris Mohar]

One of my customers is in a bit of a pickle. They need to access a ball on
a BGA chip that is already mounted on a four layer board. The ball is in
one of the inner rows. The two inner layers are power and ground. The ball
pitch is 0.8mm and the pad diameter is 0.42mm. This is a prototype fix.
Does anybody have a 0.3mm ceramic coated metal core self taping screw?


Regards,

Boris Mohar

 

[John Larkin]

One of my customers is in a bit of a pickle. They need to access a ball on
a BGA chip that is already mounted on a four layer board. The ball is in
one of the inner rows. The two inner layers are power and ground. The ball
pitch is 0.8mm and the pad diameter is 0.42mm. This is a prototype fix.
Does anybody have a 0.3mm ceramic coated metal core self taping screw?


Regards,

Boris Mohar

Why not just go in there with a tiny end mill and bore through from
the bottom to the top of the board (and pray you don't hit any signal
traces)? Then solder a wire to the ball or go in with a tiny pogo.

On all of our BGA layouts (total of *one* so far) we routed all unused
balls to a via.

John

 

[Joe Legris]

One of my customers is in a bit of a pickle. They need to access a ball on
a BGA chip that is already mounted on a four layer board. The ball is in
one of the inner rows. The two inner layers are power and ground. The ball
pitch is 0.8mm and the pad diameter is 0.42mm. This is a prototype fix.
Does anybody have a 0.3mm ceramic coated metal core self taping screw?


Regards,

Boris Mohar

Drill a large hole (maybe several mm diameter) in a trace-free and
ball-free area just inside of your target ball. Connect to it more or
less horizontally using a ball of conductive epoxy on the end of a
strand of wire. Use a bit of tape to hold it until the epoxy hardens.

Practice first on an old PCB.

 

[John Woodgate]

I read in sci.electronics.design that Boris Mohar <[email protected]>

One of my customers is in a bit of a pickle. They need to access a ball on
a BGA chip that is already mounted on a four layer board. The ball is in
one of the inner rows. The two inner layers are power and ground. The ball
pitch is 0.8mm and the pad diameter is 0.42mm. This is a prototype fix.
Does anybody have a 0.3mm ceramic coated metal core self taping screw?

Probably not, but you can fairly easily make a 0.3 mm dia glass tube by
primitive glass-working techniques and epoxy a stiff wire into it. It
MIGHT work.

 

[Mac]

I read in sci.electronics.design that Boris Mohar <[email protected]>

Probably not, but you can fairly easily make a 0.3 mm dia glass tube by
primitive glass-working techniques and epoxy a stiff wire into it. It
MIGHT work.

"Primitive glass-working techniques." Heh. That reminds me. I once
experimented with heating up disposable glass pipettes with a bunsen
burner. If you heat up a small part in the middle, you can then stretch
the pipette and the inner diameter will shrink as the hot section
stretches, until eventually the tube will close out. I think you are right
that it wouldn't be too hard, given a glass tube and a torch or bunsen
burner.

Mac

 

[Bob Stephens]

"Primitive glass-working techniques." Heh. That reminds me. I once
experimented with heating up disposable glass pipettes with a bunsen
burner. If you heat up a small part in the middle, you can then stretch
the pipette and the inner diameter will shrink as the hot section
stretches, until eventually the tube will close out. I think you are right
that it wouldn't be too hard, given a glass tube and a torch or bunsen
burner.

Mac

I met a guy in a bar once who worked for a BioMedical outfit that made
capillary tubes for blood filters. They took plastic straws about the size
of a "swizzle stick" - remember, we were in a bar - and stretched them out
until the inside diameter was the size of a blood molecule, and placed
bundles of these things inside a patient's blood vessels to filter out
impurities. They blew air throught the tube while heating and stretching it
so it wouldn't close out.

Bob

 

[John Woodgate]

"Primitive glass-working techniques." Heh. That reminds me. I once
experimented with heating up disposable glass pipettes with a bunsen
burner. If you heat up a small part in the middle, you can then stretch
the pipette and the inner diameter will shrink as the hot section
stretches, until eventually the tube will close out.

It gets mighty small before it closes out, if you don't heat the tube
too much and stretch quickly.

I think you are right
that it wouldn't be too hard, given a glass tube and a torch or bunsen
burner.

A fishtail burner is the preferred type, but I wonder if you can still
get them. They give a flat flame which allows you to heat either a small
section or a larger one, and the flame is not as hot as a Bunsen. AIUI,
there is a limited air bleed into the base of the flame, but nowhere
near as much air as in a Bunsen on 'kill'. Before the gas mantle was
invented, they were used for illumination.

Glass working is an interesting pastime for some kids, provided they
understand what 'hot' means! I suppose these days you need safety
goggles and Kevlar gloves, but it can still be fun. It's possible to
progress either to usable chemical apparatus (a 'tulip' reflux condenser
is not too difficult when some manual dexterity has been acquired) or to
art forms, such as glass animals and jewellery.

 

[Robert Sefton]

You might find it easier to make a fix if you remove the BGA first. Then
have it re-balled and re-installed after the board is reworked.

RJS

 

[ånønÿmøu§]

You might find it easier to make a fix if you remove the BGA first. Then
have it re-balled and re-installed after the board is reworked.

Ya, that sounds more like it! Or.... decap the part and maybe probe it?