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SMT electronics assembly manufacturing forum.


#11470

uBGA's | 13 May, 1999

Hi Guys,

I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say?

So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure?

Thanks a bunch,

Chrys

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Heather

#11471

Re: uBGA's | 14 May, 1999

| Hi Guys, | | I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say? | | So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure? | | Thanks a bunch, | | Chrys | Chrys,

The critical factor that I have heard about seems to be the stencil design. Talk to your stencil manufacturer for proper design guidelines. The problem is that with microBGA's the area of the aperature opening is very small compared to the area of the stencil walls and just due to physics, the paste does not release as easily. The stencil manufacturers are describing this as area ratio rather than the traditionally known aspect ratio. The aperature opening are going from a round shape towards a square shape with rounded corners to create a larger area. There is also a theory that the paste begins to release from the corners of stencil aperatures first and by creating rounded corners, the paste will have a release point. Heather Wuttke

reply »

Ryan

#11472

Re: uBGA's | 14 May, 1999

| | Hi Guys, | | | | I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say? | | | | So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure? | | | | Thanks a bunch, | | | | Chrys | | | Chrys, | | The critical factor that I have heard about seems to be the stencil design. Talk to your stencil manufacturer for proper design guidelines. The problem is that with microBGA's the area of the aperature opening is very small compared to the area of the stencil walls and just due to physics, the paste does not release as easily. The stencil manufacturers are describing this as area ratio rather than the traditionally known aspect ratio. The aperature opening are going from a round shape towards a square shape with rounded corners to create a larger area. There is also a theory that the paste begins to release from the corners of stencil aperatures first and by creating rounded corners, the paste will have a release point. | Heather Wuttke | Chrys-

I would recommend buying some 36-guage thermocouples and 0.021" drill bits to go with (use only in a drill press, with clamped board, to avoid breaking). We just got done setting up a board with 32 micro-BGAs, and 33 regular BGAs (72 total on whole board) and these two tools were indispensable for profiling these parts. Otherwise, the opening needed for a standard thermocouple is big enough to leave many uBGA balls exposed. Also, the larger thermocouples tend to move the parts when the spheres are liquid. Also, an alternative finish (gold, tin, etc.) may help a great deal because a small variation is surface flatness can leave some spheres unattached. Good Luck, Chrys! Ain't no thang!

Ryan Jennens TelGen Corporation

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Ryan

#11473

Re: uBGA's | 14 May, 1999

| | Hi Guys, | | | | I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say? | | | | So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure? | | | | Thanks a bunch, | | | | Chrys | | | Chrys, | | The critical factor that I have heard about seems to be the stencil design. Talk to your stencil manufacturer for proper design guidelines. The problem is that with microBGA's the area of the aperature opening is very small compared to the area of the stencil walls and just due to physics, the paste does not release as easily. The stencil manufacturers are describing this as area ratio rather than the traditionally known aspect ratio. The aperature opening are going from a round shape towards a square shape with rounded corners to create a larger area. There is also a theory that the paste begins to release from the corners of stencil aperatures first and by creating rounded corners, the paste will have a release point. | Heather Wuttke | Chrys-

Heather offers good advice. Also, I would recommend buying some 36-guage thermocouples and 0.021" drill bits to go with (use only in a drill press, with clamped board, to avoid breaking). We just got done setting up a board with 32 micro-BGAs, and 33 regular BGAs (72 total on whole board) and these two tools were indispensable for profiling these parts. Otherwise, the opening needed for a standard thermocouple is big enough to leave many uBGA balls exposed. Also, the larger thermocouples tend to move the parts when the spheres are liquid. Also, an alternative finish (gold, tin, etc.) may help a great deal because a small variation is surface flatness can leave some spheres unattached. Good Luck, Chrys! Ain't no thang!

Ryan Jennens TelGen Corporation

reply »

Earl Moon

#11474

Re: uBGA's | 14 May, 1999

| Hi Guys, | | I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say? | | So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure? | | Thanks a bunch, | | Chrys | Chrys,

We ran our first 1mm uBGA's about 6 months ago. The operators didn't even notice them. We run 1:1 apertures on DEK 265's with FPA and high resolution cameras. Our Fuji's have "lizzard tongues" for full arrays.

In rework, we run micro-stencils with the same apertures. The only trouble is we've seen no rework. There are other factors involved as our BTU profiles and solder paste selection - going to no-clean next month.

There's more as .8 mm stuff but little change expected but higher resolution cameras on our PNP.

Best wishes,

Earl

reply »

Philip B

#11475

Re: uBGA's | 18 May, 1999

| | Hi Guys, | | | | I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say? | | | | So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure? | | | | Thanks a bunch, | | | | Chrys | | | Chrys, | | We ran our first 1mm uBGA's about 6 months ago. The operators didn't even notice them. We run 1:1 apertures on DEK 265's with FPA and high resolution cameras. Our Fuji's have "lizzard tongues" for full arrays. | | In rework, we run micro-stencils with the same apertures. The only trouble is we've seen no rework. There are other factors involved as our BTU profiles and solder paste selection - going to no-clean next month. | | There's more as .8 mm stuff but little change expected but higher resolution cameras on our PNP. | | Best wishes, | | Earl | Earl,

I will also startup the production implementation of BGA's and uBGA's by the end of this year. I am a bit concerned about the cleaning issue with BGA's. For the moment we are still using RMA paste and we need to clean our boards (military specs). I have noticed that you will go to no-clean next month. Has this anything to do with problems of cleaning boards populated with BGA's and uBGA's?

PhilB

reply »

Earl Moon

#11476

Re: uBGA's | 18 May, 1999

| | | Hi Guys, | | | | | | I am going to be graced with the good luck of processing microBGA's in the near future. A bit of a step forward from printing 20-mil pitch and wave soldering 0805's, wouldn't you say? | | | | | | So, any of you folks who have already experienced this pleasure, could you please be so kind as to fill me in on the tips, tricks, pitfalls, etc, before I embark on my new adventure? | | | | | | Thanks a bunch, | | | | | | Chrys | | | | | Chrys, | | | | We ran our first 1mm uBGA's about 6 months ago. The operators didn't even notice them. We run 1:1 apertures on DEK 265's with FPA and high resolution cameras. Our Fuji's have "lizzard tongues" for full arrays. | | | | In rework, we run micro-stencils with the same apertures. The only trouble is we've seen no rework. There are other factors involved as our BTU profiles and solder paste selection - going to no-clean next month. | | | | There's more as .8 mm stuff but little change expected but higher resolution cameras on our PNP. | | | | Best wishes, | | | | Earl | | | Earl, | | I will also startup the production implementation of BGA's and uBGA's by the end of this year. | I am a bit concerned about the cleaning issue with BGA's. For the moment we are still using RMA paste and we need to clean our boards (military specs). I have noticed that you will go to no-clean next month. Has this anything to do with problems of cleaning boards populated with BGA's and uBGA's? | | PhilB | PhilB,

Yes and no. I mean it first is a function of economics. Then, it is a function of having to clean under the little critters (couldn't use my normal term here but it would rhyme with truckers).

I realize your concern and I wonder how you will be impacted going to no-clean. Can you really do that and meet MIL-SPEC requirements. I just can't remember all I forgot about this stuff.

Also, we're having interesting times gluing 0603's. Our latest X-Sections reveal some interesting stuff. With an acceptable toe fillet, we're OK. However, we see glue clearly under the heel fillet and sharing space with entrapped flux. When it's no-clean, no problems?, but the glue combined with the acceptable toe fillet makes for a very strong attachment. We're studying the conductivity issues more than those concerning attachment reliability over time.

I'll keep you all posted.

Earl

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