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February 2000

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Subject:
From:
Michael Fenner <[log in to unmask]>
Reply To:
Michael Fenner <[log in to unmask]>
Date:
Thu, 17 Feb 2000 21:23:33 -0000
Content-Type:
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text/plain (129 lines)
Luckily the acronym problem is sorted out, so now I suppose you are concerned with using  the
thing. Going on the descriptions I guess you are looking at reconciling processing small
interconnect pads as well as the large heatsink in the middle.

Although the centre pad is relatively large, in absolute terms 6mm is not that great and so
should not present a problem. The following might be useful:

Void free soldering on large areas is possible using SMT materials and processes and normal or
near normal parameters. The nack is to ensure good physical wetting of the surfaces you are
soldering and not to entrap air.
Use normal paste print geometries/relationships on the interconnect pads but on the large
heatsink suggest you might find it advantageous to place the paste more in  a St Andrews cross
[Saltaire] / X shape than a simple overall size reduction. IF you get your placement pressure
right this will cause the paste to spread out and sweep air out on placement and when it flows
it will continue the sweep. You will need to do some sums to get the cross section of the cross
arms  right for the metal volume you need. Again you might need to do some thermal modelling but
it is likely that you will find you can stand surprisingly large voids and still retain
sufficient thermal capacity for heatsinking, but you should aim to avoid large single voids as
these will cause stress.

Good luck

Mike

----- Original Message -----
From: John Harris <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, February 17, 2000 6:08 AM
Subject: Re: [TN] MLFP's


> Not sure what it stands for actually myself, but I will find out now. It's a
> 5Ghz QFP type device, that sits FLAT on the pcb. There are no legs or balls
> of any description, just a mirror image of the pad. In the middle of the
> device, (it's about 15mmx15mm) is a large pad about 6mmx6mm which is used as
> a heat sink, but this is also flush and also has to be soldered.
>
> Hope this describes it. Not very technical I know.
>
> John
>
> -----Original Message-----
> From:   TechNet [mailto:[log in to unmask]] On Behalf Of Stephen R. Gregory
> Sent:   Thursday, 17 February 2000 2:15 PM
> To:     [log in to unmask]
> Subject:        Re: [TN] MLFP's
>
> In a message dated 02/16/2000 8:34:39 PM Central Standard Time,
> [log in to unmask] writes:
>
> > Guys,
> >
> >  We have a requirement to run this package in fairly small runs. Anyone
> had
> >  any experience with these that they could share? I am particularly
> >  interested in issues such as presence of voids on heat transfer pad
> solder,
> >  stencil aperture design, reflow characteristics. Any info or even
> potential
> >  sources of info would be greatly appreciated. The data supplied by vendor
> >  was not really much help, only with the only suggestion being use either
> a
> 5
> >  or 6mil stencil.
> >
> >  Thanks
> >
> >  John Harris
> >  Process Engineer
> >  AEMS Pty Ltd
>
> Hi John!
>
> I guess this is one of them deals that if you have to ask what a MLFP is,
> then one won't be of much help...but I do have to ask, what is a MLFP? This
> is another of the myriad of acronyms that I'm not familiar with. Let us know
> what that is.
>
> Stencil thickness and aperture design is pretty straight forward provided
> you
> know what package you're dealing with...excuse me for my ignorance, but I
> don't know what a MLFP is....
>
> -Steve Gregory-
>
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