On Tue, 12 Jul 2011 21:55:43 -0700, mike wrote:
I practiced on a TiVo board. Had to get the air temp over 350C to get
enough heat to desolder a BGA.
Argh. Too hot. It should about 220C for leaded and about 230C for
lead free BGA.
http://www.rayprasad.com/home/rp1/page_71/smt_-_lead-free_reflow_profile_development__part_2.html
This article also covers some other issues (mixing solder types).
I then took a shot at the laptop.
The intermediate board curled up on the corner when I heated it. I
feared I'd lost connection on that corner. Probably shoulda dropped the
temp cause of the thinner intermediate board.
Again, too hot and possibly not moving the hot air gun fast enough. At
that temperature, if you stay at one position for too long, you'll
burn the board. I've reflowed similar sandwiches on JetDirect boards,
and didn't have the edges curled.
When I tried to run it, I got no video. My heart sank...
I didn't think I needed to plug in the boards for wifi, firewire
and modem, but I took a shot and reassembled the whole thing.
IT WORKS.
Hold on. Have you tried flexing the board? You may have a mechanical
contact connection, but not a soldered connection. You might also
break some other BGA connections flexing the board, so you decide if
it's worthwhile.
Got any suggestions for a blower for a hot air gun.
This Leister is a 600W element and temperature regulator
at the end of a 10-foot air hose. They ran the power wire
down the center of the air hose and it provides a lot of back pressure.
The back pressure doesn't matter much. I use a little air as
possible. The only thing the air does is move the heat from the air
gun heater, to the PCB. Too much air results in premature cooling.
Too little air doesn't move enough heat or heats too slowly. If
there's some back pressure, and the reflected air remains fairly cool,
don't worry about it.
It's designed to run off shop compressed air.
Ummm... I hope it wasn't designed to run directly off a 150 psi
manifold. Got a URL for this thing? One of these?
http://www.leister.com/en/processheat-product.html?catalog=c70f3b1c-b3d6-4c64-88be-6d7b5cdc7502
I couldn't find anything that matches your description. Perhaps if
you supplied a model number?
My 3/4HP compressor
won't supply as much flow as I like.
Assuming a piston type compressor, 3/4HP should give you about 5 cubic
ft/min. That should be enough to peel parts off the top of the board
if you get too close. No way do you need that much air for
desoldering. You're not trying to blow hot solder balls all over the
board.
I haven't found anything that
can give me more volume against the back pressure. I even tried a 14"
blower designed for blow-up advertising devices. No luck. Back pressure
just stalls the impeller and the flow drops to nearly nothing.
What size nozzle are you using? That's not normal. Looking at the
various Leister models, it appears that they were not intended for use
with a small diameter nozzle.
Can't really justify a bigger air compressor and a new circuit to run it
for this.
Does it make sense to put fans in series to get better flow under
pressure? I gots lotsa fans.
Dunno. Offhand, I don't think so.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558