Frank,
it is not really a standard document you need, it is sometimes driven
by design practices. If you require a soldermask dam between 25 mil pitch parts, then:
1. Minimum soldermask dams are 4 to 5 mils (use to be 6 mils, check with your fabshop)
2. Most design rules you grow your soldermask opening by 3 mils per side of copper pad.
So that adds up to 6 mils + 5 mil solder mask dam = 11 mils.
3. Remove 11 mils from 25 mils and you get 14 mils maximum copper pad width.
We did a quick internal study on actual component lead widths (parts from stock) versus the
manufactures part drawing.
Even though maximum width is like you say 18 mils, we never found any that were that wide. All were
darn close to nominal,
I believe plus 1 mil tolerance, none narrower.
This is what I would use to explain to your customer why side fillet is usually not required and some
cases not achievable.
If you do not require soldermask dams and are not routing on external layer between pins then give them
side fillet.
I do not think a 18 mil pad and a 13 mil lead width will create soldering problems for the assembly
shop.
Greg Scott
Cray Inc.
Frank Kimmey wrote:
> Guy,
> These are micro8 and sop packages, 25 mil pitch.
> Leads may be up to 18 mils wide, while land is only 13 mils (nominal lead
> width).
>
> All I have found so far are requirements that do not say a side fillet is
> req'd. I would like to find a standard that states a side fillet is not
> required.
>
> Thanks for the help,
> FNK
>
> Hey Steve,
> If you are watching, what is your take on side fillets?
> How do you interpret IPC-610 figure 12-71?
>
> Earl,
> comments?
>
> Werner,
> What loss in integrity and/or reliability is caused by no side fillet?
>
> Thanks to Peter and Gary for your replies, they are reinforcing my case.
>
> Frank N Kimmey, C.I.D.+
> Senior PCB Designer
> Powerwave Technologies
> PH. 916-941-3159
> Fax 916-941-3195
>
> -----Original Message-----
> From: Guy Ramsey [mailto:[log in to unmask]]
> Sent: Tuesday, May 21, 2002 5:58 AM
> To: [log in to unmask]
> Subject: Re: [TN] Side fillet requirements
>
> Something is wrong. What type of component are we discussing? Side joint
> requirments are specific to component types.
>
> If there is a compliant land pattern that is narrower than the lead width it
> would be new to me.
>
> I have seen "compliant design" reduced by undercut resulting land patterns
> like you describe.
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Frank Kimmey
> > Sent: Monday, May 20, 2002 6:17 PM
> > To: [log in to unmask]
> > Subject: [TN] Side fillet requirements
> >
> >
> > I have a customer who would like us to justify why our IPC-782 compliant
> > footprints do not allow for a side fillet (pad width is equal to
> > or smaller
> > than lead width). I did not find conclusive statement in IPC-610
> > concerning
> > this. Please help me define acceptance.
> >
> > Thanks,
> > FNK
> >
> > Frank N Kimmey, C.I.D.+
> > Senior PCB Designer
> > Powerwave Technologies
> > PH. 916-941-3159
> > Fax 916-941-3195
>
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