Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Gold Bump Flip Chip Attach

Chris Grendler

#13211

Gold Bump Flip Chip Attach | 24 December, 1998

Anyone ever attach gold bump flip chip to FR4 or Alumina substrates. Am trying to find a solder which is acceptable for use on gold. Am worried about gold imbrittlement since the gold bumps on the flip chip are .004"x.004"x.001" solid gold. The pitch on the bumps is .008" Have tried 60In/40Pb but had very poor results reflowing it. The fact is is did not reflow. Pitch is so tight that I can hardly stencil any solder onto the substrate. Using a .003" stencil. I know of a few other companies who are soldering down gold bump flip chips. They are using 60Pb/40In, .005" thick stencil with .010" appetures, and reflowing in nitrogen. Any help would be appreciated.

Thanks,

Chris Grendler

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Earl Moon

#13212

Re: Gold Bump Flip Chip Attach | 24 December, 1998

| Anyone ever attach gold bump flip chip to FR4 or Alumina substrates. Am trying to find a solder which is acceptable for use on gold. Am worried about gold imbrittlement since the gold bumps on the flip chip are .004"x.004"x.001" solid gold. The pitch on the bumps is .008" Have tried 60In/40Pb but had very poor results reflowing it. The fact is is did not reflow. Pitch is so tight that I can hardly stencil any solder onto the substrate. Using a .003" stencil. I know of a few other companies who are soldering down gold bump flip chips. They are using 60Pb/40In, .005" thick stencil with .010" appetures, and reflowing in nitrogen. Any help would be appreciated. | | Thanks, | | Chris Grendler | Only a question. Are the bumps "solid" gold or gold plated/coated?

Earl Moon

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Chris Grendler

#13213

Re: Gold Bump Flip Chip Attach | 24 December, 1998

| | Anyone ever attach gold bump flip chip to FR4 or Alumina substrates. Am trying to find a solder which is acceptable for use on gold. Am worried about gold imbrittlement since the gold bumps on the flip chip are .004"x.004"x.001" solid gold. The pitch on the bumps is .008" Have tried 60In/40Pb but had very poor results reflowing it. The fact is is did not reflow. Pitch is so tight that I can hardly stencil any solder onto the substrate. Using a .003" stencil. I know of a few other companies who are soldering down gold bump flip chips. They are using 60Pb/40In, .005" thick stencil with .010" appetures, and reflowing in nitrogen. Any help would be appreciated. | | | | Thanks, | | | | Chris Grendler | | | Only a question. Are the bumps "solid" gold or gold plated/coated? | | Earl Moon | .001" thick X.004" X .004" solid gold, not plated I wish my die vendor would supply solder bumped flip chips.

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Earl Moon

#13214

Re: Gold Bump Flip Chip Attach | 24 December, 1998

| | | Anyone ever attach gold bump flip chip to FR4 or Alumina substrates. Am trying to find a solder which is acceptable for use on gold. Am worried about gold imbrittlement since the gold bumps on the flip chip are .004"x.004"x.001" solid gold. The pitch on the bumps is .008" Have tried 60In/40Pb but had very poor results reflowing it. The fact is is did not reflow. Pitch is so tight that I can hardly stencil any solder onto the substrate. Using a .003" stencil. I know of a few other companies who are soldering down gold bump flip chips. They are using 60Pb/40In, .005" thick stencil with .010" appetures, and reflowing in nitrogen. Any help would be appreciated. | | | | | | Thanks, | | | | | | Chris Grendler | | | | | Only a question. Are the bumps "solid" gold or gold plated/coated? | | | | Earl Moon | | | .001" thick X.004" X .004" solid gold, not plated | I wish my die vendor would supply solder bumped flip chips. | | | I'd take the gold and run. What else can you do? If plated or coated, you know to remove the gold and coat what's left of your balls (hopefully brass) with tin lead.

Best of luck and wishes. There are those professing to know how to avoid the embrittlement issue. I do not because the how doesn't exist to my knowledge.

Earl Moon

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Jon Medernach

#13215

Re: Gold Bump Flip Chip Attach | 28 December, 1998

Chris, We are involved in several developments using gold stud bump attach. We make a stud bump bonder and have several processes for attach. Solder attach is best done by plating up the substrate, the underfill must be able to provide enough mechanical strength to compensate for brittle interconnect. Second method is new uses Ultrasonics. Gold bump and gold pad are attached using a new ultrasonic die bonder from KME Create group of Panasonic Factory Automation. Limited I/O of <30 and die size <5mm, but very good electrically and fast, (1.5 sec for the attach)

| Anyone ever attach gold bump flip chip to FR4 or Alumina substrates. Am trying to find a solder which is acceptable for use on gold. Am worried about gold imbrittlement since the gold bumps on the flip chip are .004"x.004"x.001" solid gold. The pitch on the bumps is .008" Have tried 60In/40Pb but had very poor results reflowing it. The fact is is did not reflow. Pitch is so tight that I can hardly stencil any solder onto the substrate. Using a .003" stencil. I know of a few other companies who are soldering down gold bump flip chips. They are using 60Pb/40In, .005" thick stencil with .010" appetures, and reflowing in nitrogen. Any help would be appreciated. | | Thanks, | | Chris Grendler |

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Earl Moon

#13216

Re: Gold Bump Flip Chip Attach | 29 December, 1998

| Chris, We are involved in several developments using gold stud bump attach. We make a stud bump bonder and have several processes for attach. Solder attach is best done by plating up the substrate, the underfill must be able to provide enough mechanical strength to compensate for brittle interconnect. Second method is new uses Ultrasonics. Gold bump and gold pad are attached using a new ultrasonic die bonder from KME Create group of Panasonic Factory Automation. Limited I/O of <30 and die size <5mm, but very good electrically and fast, (1.5 sec for the attach) | | | | Anyone ever attach gold bump flip chip to FR4 or Alumina substrates. Am trying to find a solder which is acceptable for use on gold. Am worried about gold imbrittlement since the gold bumps on the flip chip are .004"x.004"x.001" solid gold. The pitch on the bumps is .008" Have tried 60In/40Pb but had very poor results reflowing it. The fact is is did not reflow. Pitch is so tight that I can hardly stencil any solder onto the substrate. Using a .003" stencil. I know of a few other companies who are soldering down gold bump flip chips. They are using 60Pb/40In, .005" thick stencil with .010" appetures, and reflowing in nitrogen. Any help would be appreciated. | | | | Thanks, | | | | Chris Grendler | | | | Jon,

Good to see from you again. Where is your son? Is he missing in work action?

It sounds like you folks are making tremendous progress. How does the stud bump process work? The underfill seems like a good solution to the joint problems. Is it rigid, compliant, or a little of both? How does the cycles to failure analysis data look?

With ultrasonics, is this like die attach and wire bond ultrasonics but doing the whole chip at once? I mean, does the entire chip get vibrated into place by applying pressure to its top surface as part of the placement process?

Regards,

Earl Moon

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