Replacing Surface Mount ICs

[John-NZ]

There is some useful advice contained in the Philips LCD TV chassis FL9.1 Service Manual for the 32PFL3504D/F7 to 32PFL3514D/F7 models that I have not seen elesewhere. While a large service organisation might have hot-air desoldering guns with attachments to fit most integrated circuit packages, the amateur will find that the task of replacing surface mount ICs without inflicting damage to components and circuit board is not easy.

With Soldering Iron:
1. Using desoldering braid, remove the solder from all pins of the flat pack-IC. When you use solder flux which is applied to all pins of the flat pack-IC,
you can remove it easily.
2. Lift each lead of the flat pack-IC upward one by one, using a sharp pin or wire to which solder will not adhere (iron wire). When heating the pins, use
a fine tip soldering iron or a hot air desoldering machine.
3. Bottom of the flat pack-IC is fixed with glue to the CBA; when removing entire flat pack-IC, first apply soldering iron to center of the flat pack-IC and heat
up. Then remove (glue will be melted).
4. Release the flat pack-IC from the CBA using tweezers.
(to be continued!).

[John-NZ]

Re: Replacing Surface Mount ICs

With Iron Wire:
1. Using desoldering braid, remove the solder from all pins of the flat pack-IC. When you use solder flux which is applied to all pins of the flat pack-IC,
you can remove it easily.
2. Affix the wire to a workbench or solid mounting point. (Insert the free end of the iron wire under the row of pins to be lifted, at the SM IC body, and pull
on the free end as the pins are heated).
3. While heating the pins using a fine tip soldering iron or hot air blower, pull up the wire as the solder melts so as to lift the IC leads from the CBA contact pads.
4. Bottom of the flat pack-IC is fixed with glue to the CBA; when removing entire flat pack-IC, first apply soldering iron to center of the flat pack-IC and heat up.
Then remove (glue will be melted).
5. Release the flat pack-IC from the CBA using tweezers.

2. Installation
1. Using desoldering braid, remove the solder from the foil of each pin of the flat pack-IC on the CBA so you can install a replacement flat pack-IC more easily.
2. The “●” mark on the flat pack-IC indicates pin 1. Be sure this mark matches the pin 1 on the PCB when positioning for installation.
Then presolder the four corners of the flat pack-IC.
3. Solder all pins of the flat pack-IC. Be sure that none of the pins have solder bridges.
(I haven't seen the iron-wire technique before).

[John-NZ]

Re: Replacing Surface Mount ICs

Replacement of surface mount ICs and flatpack ICs is not a simple task, requiring a steady hand, a magnifier lens and experience with a good fine-tip soldering
iron. If you can not locate a coil of copper de-soldering wick/braid, a possible substitute is to strip the copper braid shield from 25cm of thin coaxial cable and
stretch it slightly before use. Cut off and discard the braid as it fills with surplus solder, or move along it to an unused area.
An alternative method for removing a damaged surface-mount IC is to cut all the pins at the IC body with a craft knife, then remove the severed pins individually
with soldering iron and tweezers. Masking tape or aluminium tape can be applied to the circuit board and components around the IC to protect them from heat.
Solder holes on circuit boards can be cleared for reuse by removing surplus solder with de-soldering braid and/or inserting a fine iron wire probe through the hole while heat is applied from the soldering iron. An old dental probe is ideal, or you can use a strand of iron spring wire (from a fine steel spring or a strand from an automotive clutch or accelerator inner cable or bicycle brake cable or stranded picture-hanging wire), or a fine steel sewing needle or pin (glued into the body of an old pen).

(There might be some useful wisdom to be passed on there, as many amateurs like myself are reluctant to replace flat-pack integrated circuits).