At 00.02 2012.07.03, you wrote:
>On Mon, Jul 2, 2012 at 5:29 PM, Electron <electron2k4@infinito.it> wrote:
>
>>
>> Hi,
>> I need to use a LGA 4x5 28L IC. Routing would be much easier in my
>> application
>> if I could put some traces beneath the chip (connect Vdd or Vss to this =
or
>> that
>> input to enable/disable functions through those pins). There's no expose=
d
>> pad.
>>
>> Will it be OK or must I route the tracks only externally? I'm afraid of
>> solder
>> bridges, etc.. expecially as I will hand solder it (the pads will protru=
de
>> and
>> I'll use a spoon-like tiny soldering tip, I've been successful with QFN
>> chips).
>>
>> Thanks for your help, this is the first time I use a LGA chip, no past
>> experience.
>> Mario
>>
>> --
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>> http://mailman.mit.edu/mailman/listinfo/piclist
>>
>
>If you have solder-mask then it should all be fine. routing under the chip=
..
> If youre hand etching boards, then 0.5mm pitch may be a bit touchy when i=
t
>comes to bridging leads, and stuff bridging underneath.
>
>
>Ive worked with similar chips (the land went all the way to the edge, but
>it still was too thin for even a fine pointed tip to touch. As far as
>soldering, with no access to the pad, but them all on the perimeter, I'd
>suggest using the hoof/gull-wing/spoon-like tip you're talking about to ti=
n
>all the pads on the IC with a small amount of solder, and then reflowing
>the chip onto your PCB.  If you dont have a hot air gun, then tin the pads
>the same, maybe a bit lighter on the solder, place it, and apply the iron
>to the extended pad, adding solder as needed for it to wet and melt the
>individual joint. with either method, all the tinning the pads on the IC
>have to be very even. The hoof tip soldering iron and a flux pen will do
>this nicely, also, some extra thin solder is very helpfull too, so you can
>control how much you add easily.
>
>If youre interested in getting hot air tools on a hobbyist budget, I'd
>reccomend http://www.circuitspecialists.com/csihotgun-2.html, plenty of
>heat, plenty of air, plenty of control, a good value imo.

Thanks, I do have a hot air rework station with interchangeable "tips" but
never really used it yet, as the few times I tried it looked less productiv=
e
than my Elsa iron station, with which I have had always very good results.

One question: should I tin only the pads of the IC or also the pads of the
PCB? When I soldered the QFN I tinned both, but I had the feeling it was to=
o
much.

Thanks,
Mario


>
>
>--=20
>Jonathan Hallameyer
>--=20
>http://www.piclist.com PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist

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View/change your membership options at
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