Hi Ramon,
Thanks for your question.
There is no plating to be carried out. The component is to be soldered
onto pads on a larger board in the usual way, except that in this case,
the base of the component consists of the 1" x 0.6" piece of fibreglass
(acting as a carrier for an IC) with copper pads underneath it. A little
like mounting a BGA except that instead of having solder balls there is
just paste, meaning that there is very little separation between the
component and the large board.
I hope that's a bit clearer.
Regards,
Jeff
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Wednesday, 23 November 2005 1:01 AM
To: [log in to unmask]
Subject: Re: [TN] Unusual soldering challenge
Hi Jeff:
I am not fully understanding. There is a small 1" X
0.6" board that has an exposed copper pad and four lands for a four
leaded surface component. The process consists of plating the pad at the
same time reflowing the leads of the part to the lands to mount it to
the board. If that is what is being done, can the pad come already
plated from the board vendor or cover with solder mask? I am just
asking.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ivanoe Pedruzzi
Sent: Tuesday, November 22, 2005 3:56 AM
To: [log in to unmask]
Subject: Re: [TN] Unusual soldering challenge
Jeff,
a grid in the aperture of a stencil of that sort is, in my experience, a
good advice.
This is the only way to keep the part seated in its position when
reflowing.
If not divided in smaller parts, the surface tension of the liquid in
that area is strong enough to re-align the part on the center of the
stenciled paste.
Besides shifting, you can't even prevent the component from rotating.
I haven't ever experienced any problem with flux entrapped nor with
boiling.
A sort of "tic-tac-toe" grid is what I was used to have in the aperture.
have a good one,
Ivan
Il giorno 22/nov/05, alle ore 06:46, Jeff Brown ha scritto:
> Hi Everyone,
>
> We have a problem with a fairly unique component that requires
> soldering to a PCB. I'm really hoping that someone has seen this
> before as it looking really awkward.
>
> The component is mounted on a piece of fiberglass about 25mm x 16mm.
> The footprint consists of a ground pad which takes up 95% of the area,
> and four signal pads with 0.5mm clearance from the ground pad.
>
> The manufacturer recommends a grid of stenciled paste for the ground
> pad due to the large area, but we are concerned that if the paste
> melts from the outside edges in, then it will at a minimum result in
> flux entrapment, and at worst, the trapped flux will boil and lift the
> component, or move the molten solder causing shorts to the signal
> pads.
>
> I imagine that even if we used solid paste pattern that this would
> probably only make the problem worse.
>
> Or are we just being overly pessimistic?
>
> Any thoughts on options would be gratefully received... Currently
> wondering about the possibility of applying BGA balls to the package
> so that there is some clearance between the board and the component.
>
> If anyone is interested, I can send the component datasheet to them
> directly.
>
> Thank you all in advance
>
> Jeff Brown and Josh Vear
> EOS Space Systems
>
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