SMC Expert Comments Desired ( Chip Masters )

[Monty]

Hi:

Tech help desired from the Chip Masters !

I generally use a Gas Bonding Station when
addressing VLSI / SMC chips when replacing
servicing later model radios.

From time to time, I always do not wish
to set up all the focus heads, and controls to repalce a 2 cent part.

I would like to know anyone out there that
perhaps has come up with other ways of replacing these parts.

A few tips I already use. With the proper
soldering / desoldering station I can
easily remove the componets, however " When
in the Field / And in emegencies ) after
removing the defective part, I use a very
tiny bit of 5min Epoxy just enough to hold
the SMC part to the board. After it dries, I then can resolder the ends, and do a general
cleaning

On larger items ( or very sensitive ones ) I
use a Small piece of Stanless Steel rod with
a Pad on one end, and then I solder the other
end to the PC Board. This will hold the part
in place when soldering. The Spring tension
is good enough to hold it in place in most
cases.

Anyhow, if there are any others who do the
same thing or have some better Ideas, I would
appreciate any extra tips for Chip Replacement in the Field.

Monty

[Elroy Jetson]

I've done some good repair work with a VERY simple and basic hot air reflow station that has a single square 10mm head. Getting the part off is of course quite easy, and here's how I prep the board to put the new one with the minimum hassle:

I take a conventional soldering iron and remove all excess solder from the PC board pads with solder wick, and then I carefully apply a minimal amount of solder to each pad, being sure to keep the amount of solder dispensed as uniform as possible. I use solder preforms (beads, usually) when possible because they are very uniform.
I use just enough solder per pad to have enough for a fully wetted connection to the part. That's usually just enough to put a slight hump on each pad, and no more.

After applying this fresh solder to the pads,
I then apply a liberal amount of paste soldering flux to the pads, and then I place the new part on the pads WITHOUT any adhesive. I center it on all the pads as carefully as possible, using tweezers and probes if required. I can handle up to .025 lead pitch components, which is as fine as they get. Then I apply the heat via the hot air station, wait until I'm totally sure that all the solder is melted and the part is hot enough, and then I gently, slowly, and carefully tap the component down to complete the solder bridges from pad to part. Of course, I use a tool to tap the part, not a finger!

Then I release pressure, and the surface tension of the solder connections will automatically center the part over its pads.
Remove the heat source, let it cool down, clean the flux, and you should be finished.

I've even have good success with those infuriating BGA (Ball Grid Array) devices, the ones that have a grid of connections on them but no pins. All the center connections are made blind. You do the best you can and you can't see any of the inner connections, but this approach works very well on them. The key is the uniform solder amounts per pad, and using the molten solder's surface tension to automatically center the part on the pads.

Elroy

[Monty]

Hi:

And a excellent tip !, and now comes the
Flux ! as not all flux works in the same
manor. I have found a old Type Solder Flux
called Sal Met ( no longer availible ) was
perfect for the applications you speak of,or
at least the ones I use.

Since Sal Met is no longer being distributed,
I use a industrial grade AMC0 60 which is a
Ethanolamine Solution, and even works well
with aluminum and perfect for copper, and
even better with plated surfaces.

Anyhow, I am looking for perhaps something
better. Please pass on the type of flux you
use, and if you use the SN63 Solder with silver content.

MS

[cathoderay]

recently came across having to replace some 48 pin smd's. which hot air device do you use? thanks bob

[Tony Soprano]

For the pros (and the shops that can afford it) it's gotta be the Chipmaster SMD-1000. For removal and installation of OMPACS and flat-pack IC's, it is indespensable. You have to pony up around $3000-4000 for this honey, but it will pay for itself very quickly. Radios that once went to Rockford are done in-house for half the price. Unit is made by APE, Automated Production Equipment. I also use their paste flux, comes in a handy hypodermic for spot application. For chip caps and resistors, a basic Weller iron and paste flux does the trick.

If you don't have a hot-air station, the Weller #6966C heat gun is a good alternative. Found in the Motorola wish book.

[johngoer]

I too use the SMD-1000 and have found it to be a very valuable tool. It is used in shop only. Had to look up Motorola's current pricing as it seemed Tony's price was low. Current Mot pricing is $5500 for the basic R1332A and $7500 for the R1333A 'Depot Pkg' which includes more heads etc plus mag light .

[Paul]

For parts with exposed connections (unlike BGA's), I'm using this method:
I remove the faulty part by applying too much solder to each side, so the pins of each side are covered alltogether. Using the soldering iron at full throttle, I keep the solder melted on all sides and using tweezers I remove the part.
I pump away the solder and clean the board using wick, so there's no solder on the board.
I place the new part and secure it by soldering with a fine tipped iron two diagonal pins. Now, if the pitch allows it, I solder one-by-one all the remaining pins (ususaly do this on QFPs). If the pitch is very fine and dense, I apply much solder, like the desoldering procedure, and afterwards I 'comb' the verticaly positioned board with the iron.
If some pins insist to stay shorted, some fresh solder can fix the job.
If the pins do insist on staying shorted, the wick is the best solution.
Some cleaning of the board afterwards is desired.
A nice example of this procedure, is the replacement of GP300's MCU.

[DJP126]

Had to look up Motorola's current pricing as it seemed Tony's price was low. Current Mot pricing is $5500 for the basic R1332A and $7500 for the R1333A 'Depot Pkg' which includes more heads etc plus mag light .

Actually, Tony's price is correct. Current Mot price for the R1319A (their lowest tier of the SMD1000) is $3868.75 with 5 more levels of systems ending with the R1334A.