Working with tsop flash

[Nick Jarmany]

Kevin,

In my experience of this type of SMD work, the most critcical issue is preserving the pads on the motherboard. Usually attempts to desolder parts whilst preserving them for re-use generally result in damage/weakening of the PCB.

To prevent this the best way is to sacrifice the soldered on part, minimising heat damage to the PCB. Use a sharp scalpel and with a controlled hand and steady force, run the pount of the blade over the chip pins along the line where they meet the chip body. Repeating this multiple times will eventually result in the chip legs becoming severed without any undue stress having been applied.

Repeat this process with the other side and lift the chip body clear.

Now you are left with two rows of renundant pins!

Use a hot iron with a broad tip and a good deal of solder. Put the iron on the pins and quicky apply solder. While feeding in solder, move iron over balance of the pins. With the whole lot molten you should be able to wipe off all the junk easily and quickly. The trick is speed - do not hesitate or loiter on anything for more than a second. Use plenty of solder and drag the "heap" quickly off the end. The surface tension of the ball of molten solder will bring everything with it, including any solder bridges between pads.

If after this you still have some shorts, use more solder and remove by dragging a ball of molten solder steadily over the pads, adding fresh solder to the ball as you go. The best way to remove solder is with more solder!

The mistake many people make with close-pitch SMD components is to use micro sized iron tips and spend ages on individual pins under microscopes. The best tactic is actually the reverse - large tip (good heat transfer), lots of solder and deal with all the pins in one operation. Our production staff can hand solder a 100-pin PQFP in under 5 seconds this way, with no shorts!

Using this technique should give you the best chance of undamaged pads onto which you can solder your socket/emulator.

Good luck!

Nick

> -----Original Message-----
> From: linuxbios-admin at clustermatic.org
> [mailto:linuxbios-admin at clustermatic.org]On Behalf Of Kevin O'Connor
> Sent: 27 September 2003 06:33
> To: linuxbios at clustermatic.org
> Subject: Working with tsop flash
> 
> 
> Hi,
> 
> I have a motherboard that I would like to get linuxbios working on.
> Unfortunately, it has a TSOP flash part that is soldered 
> directly onto it.
> I am concerned that if I write to the flash I may turn the unit into a
> "brick".
> 
> Has anyone had any experience with removing a surface mounted 
> flash TSOP
> part, and replacing it with a ZIF socket?  If I understand it 
> correctly, I
> should be able to heat up the leads of the current flash (melting the
> existing solder), extract the flash part, then solder on a zif socket
> (http://www.emulation.com/catalog/off-the-shelf_solutions/sock
ets/tsop/),
and then finally use an eprom programmer on the existing tsop flash chip if
it ever gets flashed incorrectly.  Is this correct - anyone here done this
before?  Is this procedure very tricky (can one new to soldering expect to
succeed at it)?

Any advice would be appreciated,
-Kevin

-- 
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 | Kevin O'Connor                     "BTW, IMHO we need a FAQ for      |
 | kevin at koconnor.net                  'IMHO', 'FAQ', 'BTW', etc. !"    |
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