On Sun, 4 Jan 2004 15:39:59 -0800, Garrett Mace wrote (in message ):
Here's a pic of the ROMs I want to desolder (the big chips in the photo). Identical set on identical board I want to replace...
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How do these rate on the scale of difficulty? (What are these packages?)
Thanks,
DaveC
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Garrett Mace
Those would be pretty easy to remove with the hot air gun method. I've removed hundreds of similar-sized chips from laptop motherboards. However the tough part is the proximity of those two plastic sockets; on the PCB you want to keep, you'll need to shield those somehow. Perhaps tape a couple layers of aluminum foil over them, and only heat the chips until you see the solder wet up, then quickly turn off the heat gun and flip the chips over with a dental pick. You would probably want to practice with the board you don't want to keep, and see if you can keep the plastic sockets from melting. If you can't, then maybe you should use a Chipquik or hot air pencil method.
For chips that size, and with only two side with pins, I've removed many by simply dolloping solder on and continually wiping the tip of the soldering iron along the row of pins, while keeping upward pressure on that side with a dental pick. You should be able to flex one side of the chip free from the board, then do the same thing to the other side. That always used to work with DIP packages too, but it's actually much easier on these small surface-mount chips.
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Sunny
They appear to be 44-pin SOP packages with a gull wing lead pitch of 1mm.
I would rate them as fairly easy as there is good access to the ends of the devices for introducing the stainless strip, and 1mm pitch leads are quite resistant to bending and easy to resolder without bridging (compared to 0.5mm pitch SSOP leads).
I have used the Chipquik-and-stainless-strip method successfully many times on identical parts. They might also be good candidates for the Radio Shack desolderer/Aquarium pump hot air gun (I bought the parts today but haven't assembled and tried it yet).
A
ampdoc
Hakko makes a 85W iron for desoldering flat packs. The iron is about $80.00 and all the tips run about 150.00 It is called the mach FP and is on hakko's site at:
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The trick is to tin the tip good and invert the item you are desoldering for "gravity assist". Ive been using one for sevral years and after practicing with some old PCB's for about 20 minutes have never lifted any traces or damaged a device. You can get it form East Coast Transistor
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-- Jammy Harbin J & J Electronics, Inc
227 S. 4Th St. Selmer, TN 38375
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Sunny
They appear to be 44-pin SOP packages with a gull wing lead pitch of 1mm.
I would rate them as fairly easy as there is good access to the ends of the devices for introducing the stainless strip, and 1mm pitch leads are quite resistant to bending and easy to resolder without bridging (compared to 0.5mm pitch SSOP leads).
I have used the Chipquik-and-stainless-strip method successfully many times on identical parts. They might also be good candidates for the Radio Shack desolderer/Aquarium pump hot air gun (I bought the parts today but haven't assembled and tried it yet).
M
Mat Nieuwenhoven
A radioamateur which desolders SMDs a lot told me the following technique: Take a heat-resistant, insulated wire like that used to wind transformers. Stick it behind one row of pins until it comes out on the other side, the wire should lay just behind the pins. Fasten it some way at one side (e.g. solder it), preferable somewhat in front of the line of the pins. At the other side, start heating the pins with a soldering iron, while gently pulling the free end away from the chip so that the wire pushes against the back of the pins. When the solder melts, the strain on the wire causes it to lift the pin and prevent resoldering. Move along the row of pins until all are done. Repeat as required for other sides.
Mat Nieuwenhoven
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Sunny
I have used that technique, and it's very effective if the device is slated for the dumpster after removal - although finding an anchor point is sometimes challenging. This method should not be used if you intend to re-use the device as it applies pressure at an angle to the pins and will bend them.
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