QFP's with center pads are tricky. Check the tolerance on the lead to bottom of part. We use similar parts that had a 2 to 6mil gap tolerance (and with just the large cooling plate). On the thin end you squeeze out extra solder to be trapped under the body, and thick x-ray will fail for insufficient. Defects rates could change with new lots of components. 

Making the board side pad larger eliminated loose solder balls-excess solder wets out nicely, and a step stencil for the thicker end of tolerance worked best. Now working well consistently. Having a bunch of small pads outside the cooling plate would prevent this plan and will be a big problem if the gap between body and board has variation. 

Try and find a QFN or BGA alternate.



Roger Mack



-----Original Message-----

From: TechNet <[log in to unmask]> On Behalf Of David Hillman

Sent: Thursday, June 25, 2020 11:58 AM

To: [log in to unmask]

Subject: [EXT] Re: [TN] [External] [TN] Soldering Microsemi VSC8522XJQ-02?



Hi Steve - I took a quick look at the component and if the intent of the package design is to have that center pad soldered to the assembly then run! As you mentioned, trying to get a solder paste/solder wetting balance between the center pad and the outer I/O pads is a nightmare. A QFN would be easier to solder than this package.



Dave Hillman

Collins Aerospace



On Thu, Jun 25, 2020 at 11:44 AM Steve Gregory <[log in to unmask]> wrote:



> Hi All,

>

> I just ran across a new part that I've never seen before from 

> Microsemi, it's part number VSC8522XJQ-02. Microsemi calls it a TQFP 

> package, but's not like any TQFP package I've seen. Well, actually 

> I've seen something almost like it from quite a while ago from LSI 

> Logic I think it was, they called a "Fusion" package. It had dual rows 

> of leads like this does, one set on the outer perimeter, and another 

> set inside around the middle of the body like this one does. But this 

> one has a thermal pad like a QFN and the two sets of leads are on 

> different pitches, and different types. The perimeter leads are gull 

> wing, and the inner pattern pads ar like rounded rectangle BGA pads.

>

> I remember that the fusion part took me three versions of stencils to 

> get the part to solder right even when the manufacturers 

> recommendations were first followed. I'm hoping I don't have to go 

> through that drill again with this part. I'm hoping that someone out 

> there in "Technet Land" has used this part before and can set this old fart's mind at ease...

>

> TIA,

>

> Steve

>

> --

> Steve Gregory

> Kimco Design and Manufacturing

> Process Engineer

> (208) 322-0500 Ext. -3133

>

> --

>

>

>

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