Senior Packaging Engineer
Silicon Spice Inc.
415 East Middlefield Road
Mountain View, CA 94043-4005
> -----Original Message-----
> From: email@example.com
> [mailto:firstname.lastname@example.org]On Behalf Of Dave Hoover
> Sent: Thursday, October 14, 1999 8:22 AM
> To: 'email@example.com'
> Subject: RE: [SI-LIST] : micro BGA SI vrs PCB consideration
> You can use that stack-up from a PCB fab standpoint.
> The microvias can go to layer 2 (or layer 3 or 4).
> The real issue is the following:
> 1) The microvia needs to be <=.7:1 Aspect Ratio.
> This is to guarantee the plated hole quality. (+/- 3 sigma)
> 2) The depth of the microvia needs to be evaluated from an
> assembly approach. For example, for via-in-pad will
> the microvia create a huge bubble during reflow? If so
> does the solder void violate the 20% max rule?
> I agree that for CSP (<.8mm pitch grid array packages) that
> microvia is the best approach. It allows more rout channels
> for signals.
> You can have signals on the outerlayers also. Via-in-pad
> provides more room for that. You can even have a plane
> on layer 2 with a signal on 3 to have the plane act as an
> EMI shield. (Get noisy clocks under a plane) like...
> sig (c/s)
> There are MANY reasons I've seen for MicroVias. Here's just
> a few.
> 1) Fine Pitch BGA. (Like CSP, FPBGA, DSP. Pitch's less that 1.0mm)
> 2) Via-in-pad. (To free up real estate under the BGA's so termination
> resistors and caps can be mounted as close as possible to the device)
> 3) Dropping a noisy clock/signal below a plane (to lyr 3) for EMI/EMC
> 4) Providing distributed plane capacitance right at the solder ball
> (no lead inductance which can degrade electrical performance on
> high speed devices)
> 5) Separating Logic types on the PCB on one side only with something
> else on the other. With microvias you could leave the planes intact
> with no clearances or "swiss cheese" effect.
> (i.e., Analog, Digital, RF, Control, or Microwave)
> 6) Connecting directly to planes for heat dissipation (or pwr)
> without "swiss cheesing" the plane(s).
> That's just a few. It looks like when the PCB (or substrate) get's
> greater than 130 Holes per square inch, then microvias (or
> buried/blind vias) are necessary.
> Common PCB types using microvia are:
> Portable Consumer Products
> like GPS, PDA, camcorders, PCS, and Cellular Phones.
> Interposer/Adapter Boards
> like BGA to CSP, QFP to BGA, CSP to BGA (The skys the limit here)
> Organic Chip Carrier Packages (FlipChip, PBGA, MCM-L)
> like CSP or microBGA
> Wireless Products
> like Wireless Base stations
> Memory Modules
> like SIMM
> Computer Networking Cards
> like PCI, Compact PCI, Mother Boards
> What have I forgot?
> -----Original Message-----
> From: Ilan Adar [mailto:firstname.lastname@example.org]
> Sent: Thursday, October 14, 1999 5:02 AM
> To: email@example.com
> Subject: [SI-LIST] : micro BGA SI vrs PCB consideration
> We run into some problems when using micro BGA.
> We used PTH vias between the micro BGA pads and this leads us to
> low yield in the manufacturing .
> the PCB people tell us that we must use micro via technology, but this
> requires us
> to change the PCB stack to :
> can I use such a stackup ? or is there a mother solution to micro BGA PCB
> thanks very much
> Ilan Adar
> Ilan.firstname.lastname@example.org <mailto:Ilan.email@example.com>
> tel 972-9-7751239
> Fax 972-9-7751212
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