Bryan,
I know TechNET is not for advertising BUT if you look at one of our web
pages
http://www.datumdynamics.com/exclus.html
this will give you some idea if your board is selectively solderable.
Alternatively you could email the gerber for the board to me and I will
evaluate it for you (we continually do this for our customers).
Regards
Fin
Finlay Buchan
Datum Dynamics
[log in to unmask]
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen R. Gregory
> Sent: 16 January 1999 01:14
> To: [log in to unmask]
> Subject: Re: [TN] double sided, mixed media boards
>
>
> In a message dated 1/15/99 2:43:20 PM Pacific Standard Time,
> [log in to unmask] writes:
>
> << We are assembling a small, panelized board that has all surface mount
> components on one side and all through-hole components on the other side,
> thus all solder is on one side of the board.
>
> There are 9 through-hole components on each board and there are 16 boards
> per panel. Besides doing the SMT first and then coming back and hand
> soldering the through-hole parts, how are other people doing this? Does
> anyone do the through-hole first and come back and do the SMT later? If
> so, are you using a fixture to cover the pads for the SMT parts,
> or do you
> mask, etc?
>
> Suggestions and comments are greatly appreciated.
>
> Please email response to [log in to unmask]
>
> Thanks!>>
>
> Hello there Bryan!
>
> So you got yourself a type 2C assembly huh? Just for some info to
> store away
> in the ol' memory banks:
>
> Type 1A: single side mount, PTH only
> Type 1B: single side mount, SMT only
> Type 1C: single side mount, PTH & SMT
> Type 2A: double side mount, PTH only
> Type 2B: double side mount, SMT only
> Type 2C: double side mount, PTH & SMT
>
> "Okay, that's kewl Steve, but how do I build the darn thing?"
>
> Okay, okay...don't get yer' panties all inna bunch, I'm fixing to tell
> ya'...(GRIN)
>
> There's a couple of ways you can go about this, and it depends on how the
> board was laid-out, and what kind of equipment you have. If you're auto-
> inserting your PTH, I tend to like to do that first, IF I have a glue
> dispenser. That way you don't have to worry about the parts being
> knocked off
> by the clinch and being subjected to all that banging going on
> down beneath
> the board. You auto-insert, dispense the glue, place, cure, and wave.
>
> If you don't have a dispenser, then you're left with only two
> choices, either
> stencil the epoxy first, or print paste first, then auto-insert.
> You can do
> either one, it's your choice. But for me, I'd much rather not
> deal with epoxy
> if I can help it...solder is much more robust than epoxy, and you
> don't have
> to worry so much about losing the parts you put on the backside
> in SMT before
> the board gets to wave. Now for the big if...using solder paste
> and reflowing
> the parts first, then auto-inserting means that you'll need a
> wave fixture to
> mask the surface mount on the bottom and only expose the PTH
> leads. There's a
> LOT of that going on nowdays, most of the shops that make wave
> solder fixtures
> have gotten real good at making nice fixtures to do that.
>
> But this can only be done IF there's enough clearance around the
> PTH leads to
> be able to mill an opening for the leads and still be able to seal off the
> rest of the board from the wave. For instance, if your DIP IC's have a
> decoupling cap on the bottom in between the two rows of leads,
> that's gonna be
> pretty darn difficult to machine around. But in those kinds of
> cases, where
> I've had a board that has a few parts really close to PTH and
> make it hard to
> mask off, I'll still use solder paste and make me a SMT masking
> fixture, but
> I'll dispense a dot of epoxy between the pads at those locations
> that I wasn't
> able to mask with the fixture, after the board comes out of the
> printer and
> just before placement. I do that with one of them semi-auto, foot pedal
> dispensers.
>
> When you run the board for reflow, the epoxy will cure at the
> same time, and
> you won't lose the part in the wave. If there's more than just a
> handful of
> parts that are like that, I'll just say screw it and use epoxy
> for the whole
> board...even though I don't like using it that much.
>
> I hope this'll help ya' a bit! Have a good weekend!!
>
> -Steve Gregory-
>
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