PCB Layout for BGAs

A small board with a 100QFP is being redesigned for a new FPGA due to obsolescence.  Gowin makes a 100QFP device that would be a good fit, but my customer has said "no" to the 100% Chinese brand... US government customers, ya know!  

So now I'm looking at a BGA.  I don't want to get into fine PCB design rules, so 1.0 mm ball pitch is my preference.  The only devices I can find that fit on the board have 196 or 256 pins.  But the real problem is availability.  

Digikey has a few of the XC7S15-1FTGB196I and more a scheduled for delivery in April.  Add in the various speed and temperature flavors trickling in (mostly in April) and I should be ok for the initial delivery in August... if I can get my hands on those.  I don't know if Digikey factors in the backlog orders in these counts.  

Mouser shows great inventory of Efinix parts, particularly the T13 and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in stock.  But I'd rather work with a 1.0 mm BGA.  Oddly enough, LCSC shows part numbers, but zero inventory. 

Anyone work with 0.8 mm BGAs?  What PWB feature dimensions did you use?  Did this impact the PWB cost?  

-- 

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

On 07/01/2023 18:49, gnuarm.del...@gmail.com wrote:
> A small board with a 100QFP is being redesigned for a new FPGA due to
> obsolescence.  Gowin makes a 100QFP device that would be a good fit,
> but my customer has said "no" to the 100% Chinese brand... US
> government customers, ya know!
> 
> So now I'm looking at a BGA.  I don't want to get into fine PCB
> design rules, so 1.0 mm ball pitch is my preference.  The only
> devices I can find that fit on the board have 196 or 256 pins.  But
> the real problem is availability.
> 
> Digikey has a few of the XC7S15-1FTGB196I and more a scheduled for
> delivery in April.  Add in the various speed and temperature flavors
> trickling in (mostly in April) and I should be ok for the initial
> delivery in August... if I can get my hands on those.  I don't know
> if Digikey factors in the backlog orders in these counts.
> 
> Mouser shows great inventory of Efinix parts, particularly the T13
> and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in stock.  But I'd
> rather work with a 1.0 mm BGA.  Oddly enough, LCSC shows part
> numbers, but zero inventory.
> 
> Anyone work with 0.8 mm BGAs?  What PWB feature dimensions did you
> use?  Did this impact the PWB cost?
> 

It's difficult to know the impact without knowing details of the board 
you have at the moment.  It is also somewhat dependent on the layout of 
the balls on the part - some BGA's have missing balls, or their central 
balls all connected to ground to make layout easier.

In general, 0.8 mm pitch should be doable in four layers, but you might 
need finer tracks and clearances than you used before.  In a recent 
board we did, the 0.8 mm pitch BGA was fine with four layers and normal 
vias.  We did not need to switch to 6 layers with advanced vias until we 
moved to the 0.65 mm version.

On Sunday, January 8, 2023 at 7:52:02 AM UTC-5, David Brown wrote:
> On 07/01/2023 18:49, gnuarm.del...@gmail.com wrote:=20
> > A small board with a 100QFP is being redesigned for a new FPGA due to=
=20
> > obsolescence. Gowin makes a 100QFP device that would be a good fit,=20
> > but my customer has said "no" to the 100% Chinese brand... US=20
> > government customers, ya know!=20
> >=20
> > So now I'm looking at a BGA. I don't want to get into fine PCB=20
> > design rules, so 1.0 mm ball pitch is my preference. The only=20
> > devices I can find that fit on the board have 196 or 256 pins. But=20
> > the real problem is availability.=20
> >=20
> > Digikey has a few of the XC7S15-1FTGB196I and more a scheduled for=20
> > delivery in April. Add in the various speed and temperature flavors=20
> > trickling in (mostly in April) and I should be ok for the initial=20
> > delivery in August... if I can get my hands on those. I don't know=20
> > if Digikey factors in the backlog orders in these counts.=20
> >=20
> > Mouser shows great inventory of Efinix parts, particularly the T13=20
> > and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in stock. But I'd=20
> > rather work with a 1.0 mm BGA. Oddly enough, LCSC shows part=20
> > numbers, but zero inventory.=20
> >=20
> > Anyone work with 0.8 mm BGAs? What PWB feature dimensions did you=20
> > use? Did this impact the PWB cost?=20
> >
> It's difficult to know the impact without knowing details of the board=20
> you have at the moment. It is also somewhat dependent on the layout of=20
> the balls on the part - some BGA's have missing balls, or their central=
=20
> balls all connected to ground to make layout easier.=20
>=20
> In general, 0.8 mm pitch should be doable in four layers, but you might=
=20
> need finer tracks and clearances than you used before. In a recent=20
> board we did, the 0.8 mm pitch BGA was fine with four layers and normal=
=20
> vias. We did not need to switch to 6 layers with advanced vias until we=
=20
> moved to the 0.65 mm version.

What are "normal" vias and track/space widths?  All of the BGAs I'm looking=
 at are solid arrays.  I'd give you identifiers of the packages, but I've n=
ever found standard terms.  Everyone has unique identifiers and more than o=
ne!  Packaging is insane!  I especially love how TI adds it to their data s=
heets with the reel packing and boxing data ahead of the package mechanical=
 data.  I'm sure that stuff is important to someone, but they could have a =
separate data sheet with all that.  Some companies do that with the package=
 mechanical data.  Gotta love diversity... or not.=20

My board is already 6 layers because of the high density and narrow width, =
23 mm x 115 mm.  One layer is pretty much nothing but lengthwise routing an=
d it's still very congested.  Surface layers are hard to route on.  Between=
 the parts and the vias, there's no room left.  In the new layout, a couple=
 of larger chips are going bye bye, so maybe that will improve things a bit=
.  But they are asking for some new features that will add some chips, so i=
t may be an even swap. =20

--=20

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

On 08/01/2023 20:01, gnuarm.del...@gmail.com wrote:
> On Sunday, January 8, 2023 at 7:52:02 AM UTC-5, David Brown wrote:
>> On 07/01/2023 18:49, gnuarm.del...@gmail.com wrote:
>>> A small board with a 100QFP is being redesigned for a new FPGA
>>> due to obsolescence. Gowin makes a 100QFP device that would be a
>>> good fit, but my customer has said "no" to the 100% Chinese
>>> brand... US government customers, ya know!
>>> 
>>> So now I'm looking at a BGA. I don't want to get into fine PCB 
>>> design rules, so 1.0 mm ball pitch is my preference. The only 
>>> devices I can find that fit on the board have 196 or 256 pins.
>>> But the real problem is availability.
>>> 
>>> Digikey has a few of the XC7S15-1FTGB196I and more a scheduled
>>> for delivery in April. Add in the various speed and temperature
>>> flavors trickling in (mostly in April) and I should be ok for the
>>> initial delivery in August... if I can get my hands on those. I
>>> don't know if Digikey factors in the backlog orders in these
>>> counts.
>>> 
>>> Mouser shows great inventory of Efinix parts, particularly the
>>> T13 and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in stock.
>>> But I'd rather work with a 1.0 mm BGA. Oddly enough, LCSC shows
>>> part numbers, but zero inventory.
>>> 
>>> Anyone work with 0.8 mm BGAs? What PWB feature dimensions did
>>> you use? Did this impact the PWB cost?
>>> 
>> It's difficult to know the impact without knowing details of the
>> board you have at the moment. It is also somewhat dependent on the
>> layout of the balls on the part - some BGA's have missing balls, or
>> their central balls all connected to ground to make layout easier.
>> 
>> In general, 0.8 mm pitch should be doable in four layers, but you
>> might need finer tracks and clearances than you used before. In a
>> recent board we did, the 0.8 mm pitch BGA was fine with four layers
>> and normal vias. We did not need to switch to 6 layers with
>> advanced vias until we moved to the 0.65 mm version.
> 
> What are "normal" vias and track/space widths?  All of the BGAs I'm
> looking at are solid arrays.  I'd give you identifiers of the
> packages, but I've never found standard terms.  Everyone has unique
> identifiers and more than one!  Packaging is insane!  I especially
> love how TI adds it to their data sheets with the reel packing and
> boxing data ahead of the package mechanical data.  I'm sure that
> stuff is important to someone, but they could have a separate data
> sheet with all that.  Some companies do that with the package
> mechanical data.  Gotta love diversity... or not.
> 
> My board is already 6 layers because of the high density and narrow
> width, 23 mm x 115 mm.  One layer is pretty much nothing but
> lengthwise routing and it's still very congested.  Surface layers are
> hard to route on.  Between the parts and the vias, there's no room
> left.  In the new layout, a couple of larger chips are going bye bye,
> so maybe that will improve things a bit.  But they are asking for
> some new features that will add some chips, so it may be an even
> swap.
> 

By "normal" vias I mean through-hole, without plugging or tenting - the 
cheap ones.  And by "normal" track widths and spacing, I mean the 
perhaps 6 mil - cheap sizes that any pcb manufacturer can make without 
extra charge.  Basically, at 0.8 mm BGA we didn't need to do anything 
special or consider it an especially high-density card.  It was still an 
effort to route, as there are a lot of connections in a small area.  But 
it didn't need extra cost for the pcb.

If you are already congested at 6 layers on the board, then you will 
might have to go for beyond that.  The first step is to talk to your pcb 
and board manufacturers about via-in-pad, using tented or plugged vias. 
  If you can put the vias on the pads themselves, without causing voids 
or blowouts during soldering, you can save a /lot/ of space.  Next step 
beyond that is microvias from outer layers to layers 2 and 5.  We had to 
do that for the 0.65 mm package BGA.

On Monday, January 9, 2023 at 4:02:43 AM UTC-5, David Brown wrote:
> On 08/01/2023 20:01, gnuarm.del...@gmail.com wrote:=20
> > On Sunday, January 8, 2023 at 7:52:02 AM UTC-5, David Brown wrote:=20
> >> On 07/01/2023 18:49, gnuarm.del...@gmail.com wrote:=20
> >>> A small board with a 100QFP is being redesigned for a new FPGA=20
> >>> due to obsolescence. Gowin makes a 100QFP device that would be a=20
> >>> good fit, but my customer has said "no" to the 100% Chinese=20
> >>> brand... US government customers, ya know!=20
> >>>=20
> >>> So now I'm looking at a BGA. I don't want to get into fine PCB=20
> >>> design rules, so 1.0 mm ball pitch is my preference. The only=20
> >>> devices I can find that fit on the board have 196 or 256 pins.=20
> >>> But the real problem is availability.=20
> >>>=20
> >>> Digikey has a few of the XC7S15-1FTGB196I and more a scheduled=20
> >>> for delivery in April. Add in the various speed and temperature=20
> >>> flavors trickling in (mostly in April) and I should be ok for the=20
> >>> initial delivery in August... if I can get my hands on those. I=20
> >>> don't know if Digikey factors in the backlog orders in these=20
> >>> counts.=20
> >>>=20
> >>> Mouser shows great inventory of Efinix parts, particularly the=20
> >>> T13 and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in stock.=20
> >>> But I'd rather work with a 1.0 mm BGA. Oddly enough, LCSC shows=20
> >>> part numbers, but zero inventory.=20
> >>>=20
> >>> Anyone work with 0.8 mm BGAs? What PWB feature dimensions did=20
> >>> you use? Did this impact the PWB cost?=20
> >>>=20
> >> It's difficult to know the impact without knowing details of the=20
> >> board you have at the moment. It is also somewhat dependent on the=20
> >> layout of the balls on the part - some BGA's have missing balls, or=20
> >> their central balls all connected to ground to make layout easier.=20
> >>=20
> >> In general, 0.8 mm pitch should be doable in four layers, but you=20
> >> might need finer tracks and clearances than you used before. In a=20
> >> recent board we did, the 0.8 mm pitch BGA was fine with four layers=20
> >> and normal vias. We did not need to switch to 6 layers with=20
> >> advanced vias until we moved to the 0.65 mm version.=20
> >=20
> > What are "normal" vias and track/space widths? All of the BGAs I'm=20
> > looking at are solid arrays. I'd give you identifiers of the=20
> > packages, but I've never found standard terms. Everyone has unique=20
> > identifiers and more than one! Packaging is insane! I especially=20
> > love how TI adds it to their data sheets with the reel packing and=20
> > boxing data ahead of the package mechanical data. I'm sure that=20
> > stuff is important to someone, but they could have a separate data=20
> > sheet with all that. Some companies do that with the package=20
> > mechanical data. Gotta love diversity... or not.=20
> >=20
> > My board is already 6 layers because of the high density and narrow=20
> > width, 23 mm x 115 mm. One layer is pretty much nothing but=20
> > lengthwise routing and it's still very congested. Surface layers are=20
> > hard to route on. Between the parts and the vias, there's no room=20
> > left. In the new layout, a couple of larger chips are going bye bye,=20
> > so maybe that will improve things a bit. But they are asking for=20
> > some new features that will add some chips, so it may be an even=20
> > swap.=20
> >
> By "normal" vias I mean through-hole, without plugging or tenting - the=
=20
> cheap ones. And by "normal" track widths and spacing, I mean the=20
> perhaps 6 mil - cheap sizes that any pcb manufacturer can make without=20
> extra charge. Basically, at 0.8 mm BGA we didn't need to do anything=20
> special or consider it an especially high-density card. It was still an=
=20
> effort to route, as there are a lot of connections in a small area. But=
=20
> it didn't need extra cost for the pcb.=20

So you don't know what size ball pad, via pad/drill and trace/space you act=
ually used?  I'm finding it a bit harder than I expected to figure out dime=
nsions that work.  I'd love to use the Xilinx 196 ball, 1.0 mm pitch part, =
but they are still pretty hard to get.  Efinix has nothing but smaller pitc=
h BGAs.  256 ball, 0.8 mm pitch, or 169 ball, 0.65 mm pitch.  0.65 mm pitch=
 just won't work for me. =20


> If you are already congested at 6 layers on the board, then you will=20
> might have to go for beyond that. The first step is to talk to your pcb=
=20
> and board manufacturers about via-in-pad, using tented or plugged vias.=
=20
> If you can put the vias on the pads themselves, without causing voids=20
> or blowouts during soldering, you can save a /lot/ of space. Next step=20
> beyond that is microvias from outer layers to layers 2 and 5. We had to=
=20
> do that for the 0.65 mm package BGA.

Absolutely not interested in 0.65 mm pitch, or any of the high density tech=
niques like via in pad. =20

I can get away with nearly no vias, if I can route two traces between pins.=
  That works at 1.0 mm, but at 0.8 mm, the trace/space has to be pretty sma=
ll. =20

JLCPCB lists 0.2 mm drill (8 mil) and 0.45 mm via pads (18 mil).   Assuming=
 BGA lands of 0.4 mm means you can route 2 traces between pads only with 0.=
08 mm (3.2 mil) trace/space.  Routing between the via holes is also tight, =
with trace/space of 0.08 mm (3.2 mil) and 0.13 mm (5.1 mil) (according to X=
ilinx).  I've read elsewhere that the space to the via drill should be 0.2 =
mm (8 mil) minimum for lower cost boards, so this doesn't sound good for ro=
uting two traces.  With that restriction, I could only route two rows of pi=
ns without vias.  Adding vias to escape the BGA makes the entire section of=
 the board a difficult for routing. =20

Yeah, I'd much prefer to go with a 1.0 mm part like the Xilinx 196 ball Spa=
rtan 7 parts.  I just don't know if I'll be able to get them.=20

--=20

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

On 09/01/2023 11:42, gnuarm.del...@gmail.com wrote:
> On Monday, January 9, 2023 at 4:02:43 AM UTC-5, David Brown wrote:
>> On 08/01/2023 20:01, gnuarm.del...@gmail.com wrote:
>>> On Sunday, January 8, 2023 at 7:52:02 AM UTC-5, David Brown
>>> wrote:
>>>> On 07/01/2023 18:49, gnuarm.del...@gmail.com wrote:
>>>>> A small board with a 100QFP is being redesigned for a new
>>>>> FPGA due to obsolescence. Gowin makes a 100QFP device that
>>>>> would be a good fit, but my customer has said "no" to the
>>>>> 100% Chinese brand... US government customers, ya know!
>>>>> 
>>>>> So now I'm looking at a BGA. I don't want to get into fine
>>>>> PCB design rules, so 1.0 mm ball pitch is my preference. The
>>>>> only devices I can find that fit on the board have 196 or 256
>>>>> pins. But the real problem is availability.
>>>>> 
>>>>> Digikey has a few of the XC7S15-1FTGB196I and more a
>>>>> scheduled for delivery in April. Add in the various speed and
>>>>> temperature flavors trickling in (mostly in April) and I
>>>>> should be ok for the initial delivery in August... if I can
>>>>> get my hands on those. I don't know if Digikey factors in the
>>>>> backlog orders in these counts.
>>>>> 
>>>>> Mouser shows great inventory of Efinix parts, particularly
>>>>> the T13 and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in
>>>>> stock. But I'd rather work with a 1.0 mm BGA. Oddly enough,
>>>>> LCSC shows part numbers, but zero inventory.
>>>>> 
>>>>> Anyone work with 0.8 mm BGAs? What PWB feature dimensions
>>>>> did you use? Did this impact the PWB cost?
>>>>> 
>>>> It's difficult to know the impact without knowing details of
>>>> the board you have at the moment. It is also somewhat dependent
>>>> on the layout of the balls on the part - some BGA's have
>>>> missing balls, or their central balls all connected to ground
>>>> to make layout easier.
>>>> 
>>>> In general, 0.8 mm pitch should be doable in four layers, but
>>>> you might need finer tracks and clearances than you used
>>>> before. In a recent board we did, the 0.8 mm pitch BGA was fine
>>>> with four layers and normal vias. We did not need to switch to
>>>> 6 layers with advanced vias until we moved to the 0.65 mm
>>>> version.
>>> 
>>> What are "normal" vias and track/space widths? All of the BGAs
>>> I'm looking at are solid arrays. I'd give you identifiers of the 
>>> packages, but I've never found standard terms. Everyone has
>>> unique identifiers and more than one! Packaging is insane! I
>>> especially love how TI adds it to their data sheets with the reel
>>> packing and boxing data ahead of the package mechanical data. I'm
>>> sure that stuff is important to someone, but they could have a
>>> separate data sheet with all that. Some companies do that with
>>> the package mechanical data. Gotta love diversity... or not.
>>> 
>>> My board is already 6 layers because of the high density and
>>> narrow width, 23 mm x 115 mm. One layer is pretty much nothing
>>> but lengthwise routing and it's still very congested. Surface
>>> layers are hard to route on. Between the parts and the vias,
>>> there's no room left. In the new layout, a couple of larger chips
>>> are going bye bye, so maybe that will improve things a bit. But
>>> they are asking for some new features that will add some chips,
>>> so it may be an even swap.
>>> 
>> By "normal" vias I mean through-hole, without plugging or tenting -
>> the cheap ones. And by "normal" track widths and spacing, I mean
>> the perhaps 6 mil - cheap sizes that any pcb manufacturer can make
>> without extra charge. Basically, at 0.8 mm BGA we didn't need to do
>> anything special or consider it an especially high-density card. It
>> was still an effort to route, as there are a lot of connections in
>> a small area. But it didn't need extra cost for the pcb.
> 
> So you don't know what size ball pad, via pad/drill and trace/space
> you actually used?  I'm finding it a bit harder than I expected to
> figure out dimensions that work.  I'd love to use the Xilinx 196
> ball, 1.0 mm pitch part, but they are still pretty hard to get.
> Efinix has nothing but smaller pitch BGAs.  256 ball, 0.8 mm pitch,
> or 169 ball, 0.65 mm pitch.  0.65 mm pitch just won't work for me.
> 

I'm afraid I don't remember the sizes used - I was not directly involved 
in the layout and routing.  (I've done fine-pitched BGA layout, but it's 
probably 15 years since I did a pcb design myself.)

Is it the routing you see as a problem for 0.65 mm pitch, or the cost of 
boards with high density features, or the production of them?  We have 
found that while the 0.65 mm pitch parts were harder for the layout and 
a little more expensive for the boards, parts in these packages can be a 
lot easier to get hold of.  The choice of 0.65 mm or 0.8 mm was forced 
by component availability, rather than as a preference by our layout 
folk.  (Our production people have no qualms about mounting small pitch 
BGAs.)

> 
>> If you are already congested at 6 layers on the board, then you
>> will might have to go for beyond that. The first step is to talk to
>> your pcb and board manufacturers about via-in-pad, using tented or
>> plugged vias. If you can put the vias on the pads themselves,
>> without causing voids or blowouts during soldering, you can save a
>> /lot/ of space. Next step beyond that is microvias from outer
>> layers to layers 2 and 5. We had to do that for the 0.65 mm package
>> BGA.
> 
> Absolutely not interested in 0.65 mm pitch, or any of the high
> density techniques like via in pad.
> 
> I can get away with nearly no vias, if I can route two traces between
> pins.  That works at 1.0 mm, but at 0.8 mm, the trace/space has to be
> pretty small.
> 
> JLCPCB lists 0.2 mm drill (8 mil) and 0.45 mm via pads (18 mil).
> Assuming BGA lands of 0.4 mm means you can route 2 traces between
> pads only with 0.08 mm (3.2 mil) trace/space.  Routing between the
> via holes is also tight, with trace/space of 0.08 mm (3.2 mil) and
> 0.13 mm (5.1 mil) (according to Xilinx).  I've read elsewhere that
> the space to the via drill should be 0.2 mm (8 mil) minimum for lower
> cost boards, so this doesn't sound good for routing two traces.  With
> that restriction, I could only route two rows of pins without vias.
> Adding vias to escape the BGA makes the entire section of the board a
> difficult for routing.
> 

Mechanical drilling has a lot bigger tolerances than laser drilling, so 
you do need to have extra space between the via hole and tracks on the 
internal layers to account for the inaccuracies.  Some manufacturers 
will give you tighter specifications - in particular, some use lasers 
for 0.2 mm holes.  (And some, on the other hand, use mechanical drills 
and charge extra for 0.2 mm holes due to extra breakage of the small 
drill bits.)

> Yeah, I'd much prefer to go with a 1.0 mm part like the Xilinx 196
> ball Spartan 7 parts.  I just don't know if I'll be able to get
> them.
> 

That's always the big problem these days.  I'm afraid I can't give much 
advice there (at least, nothing that you won't already have thought of 
yourself) - we are all in the same boat.

gnuarm.del...@gmail.com <gnuarm.deletethisbit@gmail.com> wrote:
> Anyone work with 0.8 mm BGAs?  What PWB feature dimensions did you use? 
> Did this impact the PWB cost?

I've not done this for real, but I did a bit of playing around with PCB
routing such BGA FPGAs.  I was trying to see if it was feasible to use them
on cheap PCB processes with basic soldering (I never actually made any
boards to test it).  One of the limitations of cheap processes is the
tolerances can be quite slack: eg 6mil track width/spacing, which makes
doing the BGA escapes hard.

An interesting (to me) observation was that you may be able to make PCB
routing easier by choosing your pinout wisely - eg don't route signals from
inner or adjacent balls where you don't need them.  That means it wasn't
such a headache to have more pins because you can ignore many of them.  For
some of them, it was fine to short adjacent pins to (safe) power rails if it
wasn't possible to separate them.

Another observation was that it might be fine to have a net route through
unused pins if they're all high impedance in the FPGA config.  I'd not do
this for fast signals, but maybe OK for slow/static ones.

Not ideal, but a couple of tricks where FPGAs offer a little bit more PCB
routing flexibility compared with off the shelf parts.

Theo

On Monday, January 9, 2023 at 7:42:20 AM UTC-5, David Brown wrote:
> On 09/01/2023 11:42, gnuarm.del...@gmail.com wrote:=20
> > On Monday, January 9, 2023 at 4:02:43 AM UTC-5, David Brown wrote:=20
> >> On 08/01/2023 20:01, gnuarm.del...@gmail.com wrote:=20
> >>> On Sunday, January 8, 2023 at 7:52:02 AM UTC-5, David Brown=20
> >>> wrote:=20
> >>>> On 07/01/2023 18:49, gnuarm.del...@gmail.com wrote:=20
> >>>>> A small board with a 100QFP is being redesigned for a new=20
> >>>>> FPGA due to obsolescence. Gowin makes a 100QFP device that=20
> >>>>> would be a good fit, but my customer has said "no" to the=20
> >>>>> 100% Chinese brand... US government customers, ya know!=20
> >>>>>=20
> >>>>> So now I'm looking at a BGA. I don't want to get into fine=20
> >>>>> PCB design rules, so 1.0 mm ball pitch is my preference. The=20
> >>>>> only devices I can find that fit on the board have 196 or 256=20
> >>>>> pins. But the real problem is availability.=20
> >>>>>=20
> >>>>> Digikey has a few of the XC7S15-1FTGB196I and more a=20
> >>>>> scheduled for delivery in April. Add in the various speed and=20
> >>>>> temperature flavors trickling in (mostly in April) and I=20
> >>>>> should be ok for the initial delivery in August... if I can=20
> >>>>> get my hands on those. I don't know if Digikey factors in the=20
> >>>>> backlog orders in these counts.=20
> >>>>>=20
> >>>>> Mouser shows great inventory of Efinix parts, particularly=20
> >>>>> the T13 and T20 in a 0.8 mm 256 pin BGA, 10s of thousands in=20
> >>>>> stock. But I'd rather work with a 1.0 mm BGA. Oddly enough,=20
> >>>>> LCSC shows part numbers, but zero inventory.=20
> >>>>>=20
> >>>>> Anyone work with 0.8 mm BGAs? What PWB feature dimensions=20
> >>>>> did you use? Did this impact the PWB cost?=20
> >>>>>=20
> >>>> It's difficult to know the impact without knowing details of=20
> >>>> the board you have at the moment. It is also somewhat dependent=20
> >>>> on the layout of the balls on the part - some BGA's have=20
> >>>> missing balls, or their central balls all connected to ground=20
> >>>> to make layout easier.=20
> >>>>=20
> >>>> In general, 0.8 mm pitch should be doable in four layers, but=20
> >>>> you might need finer tracks and clearances than you used=20
> >>>> before. In a recent board we did, the 0.8 mm pitch BGA was fine=20
> >>>> with four layers and normal vias. We did not need to switch to=20
> >>>> 6 layers with advanced vias until we moved to the 0.65 mm=20
> >>>> version.=20
> >>>=20
> >>> What are "normal" vias and track/space widths? All of the BGAs=20
> >>> I'm looking at are solid arrays. I'd give you identifiers of the=20
> >>> packages, but I've never found standard terms. Everyone has=20
> >>> unique identifiers and more than one! Packaging is insane! I=20
> >>> especially love how TI adds it to their data sheets with the reel=20
> >>> packing and boxing data ahead of the package mechanical data. I'm=20
> >>> sure that stuff is important to someone, but they could have a=20
> >>> separate data sheet with all that. Some companies do that with=20
> >>> the package mechanical data. Gotta love diversity... or not.=20
> >>>=20
> >>> My board is already 6 layers because of the high density and=20
> >>> narrow width, 23 mm x 115 mm. One layer is pretty much nothing=20
> >>> but lengthwise routing and it's still very congested. Surface=20
> >>> layers are hard to route on. Between the parts and the vias,=20
> >>> there's no room left. In the new layout, a couple of larger chips=20
> >>> are going bye bye, so maybe that will improve things a bit. But=20
> >>> they are asking for some new features that will add some chips,=20
> >>> so it may be an even swap.=20
> >>>=20
> >> By "normal" vias I mean through-hole, without plugging or tenting -=20
> >> the cheap ones. And by "normal" track widths and spacing, I mean=20
> >> the perhaps 6 mil - cheap sizes that any pcb manufacturer can make=20
> >> without extra charge. Basically, at 0.8 mm BGA we didn't need to do=20
> >> anything special or consider it an especially high-density card. It=20
> >> was still an effort to route, as there are a lot of connections in=20
> >> a small area. But it didn't need extra cost for the pcb.=20
> >=20
> > So you don't know what size ball pad, via pad/drill and trace/space=20
> > you actually used? I'm finding it a bit harder than I expected to=20
> > figure out dimensions that work. I'd love to use the Xilinx 196=20
> > ball, 1.0 mm pitch part, but they are still pretty hard to get.=20
> > Efinix has nothing but smaller pitch BGAs. 256 ball, 0.8 mm pitch,=20
> > or 169 ball, 0.65 mm pitch. 0.65 mm pitch just won't work for me.=20
> >
> I'm afraid I don't remember the sizes used - I was not directly involved=
=20
> in the layout and routing. (I've done fine-pitched BGA layout, but it's=
=20
> probably 15 years since I did a pcb design myself.)=20
>=20
> Is it the routing you see as a problem for 0.65 mm pitch, or the cost of=
=20
> boards with high density features, or the production of them? We have=20
> found that while the 0.65 mm pitch parts were harder for the layout and=
=20
> a little more expensive for the boards, parts in these packages can be a=
=20
> lot easier to get hold of. The choice of 0.65 mm or 0.8 mm was forced=20
> by component availability, rather than as a preference by our layout=20
> folk. (Our production people have no qualms about mounting small pitch=20
> BGAs.)

I'm trying to be as conservative as possible.  I'd rather not use BGAs at a=
ll, but the only QFPs I can find that fit on the board are Gowin, which is =
not on the approved vendor list with my customer.  They are too Chinese. =
=20

I'm concerned about adding cost for the boards, cost for the assembly and j=
ust an easy road forward.  I spend the last two years building 8,000 units =
when the CODEC factory burnt down.  The customer knows about this issue, bu=
t the previous CM turned flaky on me and all but stopped delivering product=
. =20

I have a new CM, but I don't want to go through production problems again. =
=20


> >> If you are already congested at 6 layers on the board, then you=20
> >> will might have to go for beyond that. The first step is to talk to=20
> >> your pcb and board manufacturers about via-in-pad, using tented or=20
> >> plugged vias. If you can put the vias on the pads themselves,=20
> >> without causing voids or blowouts during soldering, you can save a=20
> >> /lot/ of space. Next step beyond that is microvias from outer=20
> >> layers to layers 2 and 5. We had to do that for the 0.65 mm package=20
> >> BGA.=20
> >=20
> > Absolutely not interested in 0.65 mm pitch, or any of the high=20
> > density techniques like via in pad.=20
> >=20
> > I can get away with nearly no vias, if I can route two traces between=
=20
> > pins. That works at 1.0 mm, but at 0.8 mm, the trace/space has to be=20
> > pretty small.=20
> >=20
> > JLCPCB lists 0.2 mm drill (8 mil) and 0.45 mm via pads (18 mil).=20
> > Assuming BGA lands of 0.4 mm means you can route 2 traces between=20
> > pads only with 0.08 mm (3.2 mil) trace/space. Routing between the=20
> > via holes is also tight, with trace/space of 0.08 mm (3.2 mil) and=20
> > 0.13 mm (5.1 mil) (according to Xilinx). I've read elsewhere that=20
> > the space to the via drill should be 0.2 mm (8 mil) minimum for lower=
=20
> > cost boards, so this doesn't sound good for routing two traces. With=20
> > that restriction, I could only route two rows of pins without vias.=20
> > Adding vias to escape the BGA makes the entire section of the board a=
=20
> > difficult for routing.=20
> >
> Mechanical drilling has a lot bigger tolerances than laser drilling, so=
=20
> you do need to have extra space between the via hole and tracks on the=20
> internal layers to account for the inaccuracies. Some manufacturers=20
> will give you tighter specifications - in particular, some use lasers=20
> for 0.2 mm holes. (And some, on the other hand, use mechanical drills=20
> and charge extra for 0.2 mm holes due to extra breakage of the small=20
> drill bits.)

JLCPCB does 0.2 mm holes without extra charge, along with 0.45 mm via pads.=
  They charge a bit extra for 0.4 mm pads.  I guess it makes for a smaller =
target.  I look at various PCB maker's pages to see what they state they ca=
n do.=20


> > Yeah, I'd much prefer to go with a 1.0 mm part like the Xilinx 196=20
> > ball Spartan 7 parts. I just don't know if I'll be able to get=20
> > them.=20
> >
> That's always the big problem these days. I'm afraid I can't give much=20
> advice there (at least, nothing that you won't already have thought of=20
> yourself) - we are all in the same boat.

Yeah, I need to get in touch with a real distributor, rather than the web g=
uys.  Someone who has a sales person who will work with me.  I remember in =
1999, when I started working for myself, the sales people were dying to get=
 their foot in the door.  They quoted me great prices!  Now, not so much.=
=20

--=20

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

On 2023-01-09 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
>
> I'm trying to be as conservative as possible.  I'd rather not use BGAs at all, but the only QFPs I can find that fit on the board are Gowin, which is not on the approved vendor list with my customer.  They are too Chinese.  
>

Digikey has a number of FPGAs in QFP100/144 in stock. Efinix,
Microchip, Lattice, Xilinx. Nothing that suits your needs?

-- 
Stef

Kinkler's First Law:
	Responsibility always exceeds authority.

Kinkler's Second Law:
	All the easy problems have been solved.

On Monday, January 9, 2023 at 7:30:34 PM UTC-5, Stef wrote:
> On 2023-01-09 gnuarm.del...@gmail.com wrote in comp.arch.fpga: 
> > 
> > I'm trying to be as conservative as possible. I'd rather not use BGAs at all, but the only QFPs I can find that fit on the board are Gowin, which is not on the approved vendor list with my customer. They are too Chinese. 
> >
> Digikey has a number of FPGAs in QFP100/144 in stock. Efinix, 
> Microchip, Lattice, Xilinx. Nothing that suits your needs? 

The QFP144 is far too large.  Efinix has no QFP100 parts.  Lattice has no QFP100 parts that I've seen since the LFXP parts revision 2.0 of my board used.  Xilinx has not had any in decades, unless you mean the very small, yet expensive CPLD thing they sell.  Microchip might have some QFP100 parts in one of their older lines that I'm not so familiar with.  I believe their logic cells can be either logic, or FFs, but not both.   So you need roughly double the count, if not more.  They are very expensive too.  I've never been inclined to research such an old product, much like the Spartan 3.  I get that in a QFP100, but how long will they continue to make Spartan 3 devices... which have also climbed significantly in price.  It's what is called NRND.  Gowin would have been perfect, but at one point they were put on a US list of CCMC (Communist Chinese Military Companies).  Even though they were taken off, my customer sells a lot to the US government, so they don't like the "optics". 

Did I miss any?  

Trust me, I've been traveling this road for the last eight years from when Lattice first announced the end of the line for the LFXP parts.  Surprisingly, I noticed the other day that Arrow, who invested heavily in the line when Lattice announced EOL, still has almost 30,000 of them.  In theory, I could continue to use those, but I do expect to sell more than 30,000 over the next 10 years.  In fact, I am going to turn this over to a CM, who will in turn, pay me a royalty for every unit shipped.  Other than consulting, I will be out of the business, but still receive payments for everything sold.  I won't be the guy worrying about where to find what part! 

At this point, I'd be happy with the Xilinx XC7S15-1FTGB196I.  Digikey has over 800 in stock which is more than half of what I need.  They claim they will have the rest by April.  I just don't know how to get on the list to receive them.  I guess the fact that they have inventory, means no one is in line to get the April lot.  I really need to talk to someone who can give me straight answers about the future availability though.  It would not help to design in a part that let's me ship the first order, then not receive any parts for the next year! 

-- 

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209