Pitch and Power Packaging Considerationsewh.ieee.org/soc/cpmt/presentations/cpmt0611a.pdf · presentation on 40 - 50 micron pitch flip chip bumping a few months ago. • In 2000 I

Santa Clara Valley Chapter, CPMT Society

Wednesday, November 8, 2006

1

© John Burke 2006 +1(408) 515 4992

Pitch and PowerPackaging Considerations

Presented by John Burke – Optichron Inc

IEEE CPMT Dinner November 8 2006

© John Burke 2006 +1(408) 515 4992

Background• This paper was prepared as a result of the IEEE

presentation on 40 - 50 micron pitch flip chip bumping a few months ago.

• In 2000 I rationalized that eventually the pitch of a bumped die would start to impact the substrate ability to resolve the interconnection pitch through regular board technology and also start to impact the accuracy/cost of the placement machines used to position the die.

• At that time I applied for a patent through the company that I worked for Saturn Electronics and Engineering for a patent on a traceless flip chip technology for flexible circuit assembly.



2

© John Burke 2006 +1(408) 515 4992

Background• More recently I have been considering how to improve

the thermal performance of BGA and similar packages.• Both of these concepts are presented in outline here for

your comments and critique.

© John Burke 2006 +1(408) 515 4992

Traceless flip chip• Having worked on flip chip technology for number of

years – in 2000 I rationalized that if the bumping process got to the level where the pitch was achieving 50 microns pitch or less it would present some sever challenges for the assembly industry in two major areas:

– Placement accuracy– Circuit board production

• The ideas that follow represent the results of the thought process that set out to eliminate both of these issues at finer bumped die pitches.



3

© John Burke 2006 +1(408) 515 4992

Conventional trace/pad layoutFlip chip Die

“lollipop” pads

Bumps

© John Burke 2006 +1(408) 515 4992

Traceless trace/”pad” layoutNo pads – solid “picture frame”



4

© John Burke 2006 +1(408) 515 4992

Conventional trace/pad theta issue

© John Burke 2006 +1(408) 515 4992

Traceless trace/”pad” theta issue



5

© John Burke 2006 +1(408) 515 4992

So you made a short circuit – Big Deal

• So at this point we have an assembly with all die connections shorted together.

• We now have to “find” the die interconnection points which we can only reasonably do – yes you guessed it –by X-ray.

© John Burke 2006 +1(408) 515 4992

Assembly is X ray imaged

We use a real time X-ray to locate the interconnect points between the die bumps and the “picture frame. This is referenced back to fiducials on the flex assembly.

+

+



6

© John Burke 2006 +1(408) 515 4992

Assembly is X ray imaged

Using the co-ordinate data the polyamide is opened and the copper excised using lasers between the traces from the non die side of the flex assembly

© John Burke 2006 +1(408) 515 4992

Conventional trace/pad misaligned



7

© John Burke 2006 +1(408) 515 4992

Traceless trace/”pad” misaligned

© John Burke 2006 +1(408) 515 4992

Trials run• In 2000 the only tests that could be run were actually to

open up the polyimide and cut the trace patterns in the copper

• Due to the lack of 40 micron pitch die in 2000 these experiments were actually carried out using regular bump pitches to prove the process.

• Additionally trials were run in slicing the interconnect at a 40 micron pitch using a 3rd party laser service.

• Both trials were successful



8

© John Burke 2006 +1(408) 515 4992

Timing• This technology was visualized as a replacement for

TAB in Flex, and as an automated reel to reel process.

• In 2000 it was obvious that it was going to be a technology of the future.

• With the advent of 40 – 50 micron bumping it may be about to mature.

© John Burke 2006 +1(408) 515 4992

Thoughts on BGA Heat Extraction

• Everyone has heard the expression of squeezing a quart into a pint pot. In electronics we are trying in some cases to extract a quart out of a pint pot.

• Thermally that's about where we are at with BGA technology. If you look at the slides on the following pages you can see that all variants of BGA packaging are generally aimed at one thing – getting more heat out of the package.



9

© John Burke 2006 +1(408) 515 4992

Conventional BGA packages

© John Burke 2006 +1(408) 515 4992

Conventional BGA packages



10

© John Burke 2006 +1(408) 515 4992

So what about a better mouse trap?

• I got to looking at the various solutions and realized that all of the better thermal enhanced packages were either flip chip or mounted bonding side down.

• This is not an issue for your first run unless you may want to FIB the chip……to correct things on the proto’s

© John Burke 2006 +1(408) 515 4992

So what about a better mouse trap?

• I looked around and realized that on the regular less expensive HS – PBGA, XP-FPGA etc. that the main barrier was the molding compound.

• Companies have various solutions to this including dummy silicon sat on top of the die to pipe the heat to the outside heat spreader.

• Unfortunately most of the solutions that involve the use of this type of solution have a rather poor yield since the dummy die has to be incorporated into the assembly during the molding process and this can lead to excessive forces on the active die causing cracking issues.



11

© John Burke 2006 +1(408) 515 4992

HE- PBGA Assembly Flow

Base interconnect layerDie

Wire bonds

© John Burke 2006 +1(408) 515 4992



Wire bondsHeat Spreader



12

© John Burke 2006 +1(408) 515 4992


Injection mold bottom Die set

Injection mold top Die set



© John Burke 2006 +1(408) 515 4992


Molding compound







13

© John Burke 2006 +1(408) 515 4992

HTE- PBGA Assembly Flow


Wire bonds

© John Burke 2006 +1(408) 515 4992



Wire bondsStepped Heat Spreader

Phase Change Material



14

© John Burke 2006 +1(408) 515 4992



Wire bondsStepped Heat SpreaderPhase Change

Material

© John Burke 2006 +1(408) 515 4992

HTE- PBGA Assembly FlowPlastic Injection Inlet





Material

Gap



15

© John Burke 2006 +1(408) 515 4992

HTE- PBGA Assembly FlowPlastic Injection Inlet





Material

© John Burke 2006 +1(408) 515 4992


Molding compound

Plastic Injection Inlet




Wire bondsStepped Heat

SpreaderPhase Change Material



16

© John Burke 2006 +1(408) 515 4992


Solder Connections


Wire bondsStepped Heat

SpreaderPhase Change Material

© John Burke 2006 +1(408) 515 4992

Thought 2

130140150

Go back and take another look at the problem………8-)



17

© John Burke 2006 +1(408) 515 4992

Thought 2 process flow…!


Wire bonds

© John Burke 2006 +1(408) 515 4992

Thought 2 process flow…!Tooling extension

Compliant material on tool tip





Wire bonds



18

© John Burke 2006 +1(408) 515 4992







Wire bonds

© John Burke 2006 +1(408) 515 4992







Wire bonds

Molding compound



19

© John Burke 2006 +1(408) 515 4992



Wire bonds

Molding compound

Open cavity after molding process

© John Burke 2006 +1(408) 515 4992



Wire bonds

T section Heat-Sprink -radial copper areas with

through holes

Mechanical bond

Thermally conductive compound

Molding compound



20

© John Burke 2006 +1(408) 515 4992

Top View Enterprise PackageRadial copper

arms

Through holes to increase air

thermal transfer

Molding compound

Gap on lower side to increase

air flow

© John Burke 2006 +1(408) 515 4992

Enterprise CarrierRadial copper

arms

Through holes to increase air

thermal transfer

Gap on lower side to increase

air flow

Full area Heat-Sprink for maximum transfer



21

© John Burke 2006 +1(408) 515 4992

Pitch and PowerPackaging Considerations

Presented by John BurkeIEEE CPMT Dinner November 8 2006

Thank you for your time – Any Questions?

Documents

Pitch and Power Packaging Considerationsewh.ieee.org/soc/cpmt/presentations/cpmt0611a.pdf · presentation on 40 - 50 micron pitch flip chip bumping a few months ago. • In 2000 I