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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Earl Moon

#12393

BGA repair/rework | 6 March, 1999

I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier) using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between.

Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or place and reflow two parts in sequence while the third does not budge or reflow all around the perimeter.

This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with this phenomonon (I said something like it again)?

I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing similar repairs to lesser boards - as 8 layers compared with the 16's here.

My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air "blanketing" the board's bottom surface though many device edges are very close to the board's edges (.100" or less) and other design rule violations. This does not allow the "blanket" to provide the same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on "real" boards.

I am keying on part removal success with outside T/C's attached closely to part corners to ensure I start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500 boards. Anyway, is there anyone capable of offering objective suggestions concerning this type behaviour.

Earl Moon

reply »

Dean

#12394

Re: BGA repair/rework | 6 March, 1999

| | I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier) using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between. | | Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or place and reflow two parts in sequence while the third does not budge or reflow all around the | perimeter. | | This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with this phenomonon (I said something like it again)? | | I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing similar repairs to lesser boards - as 8 layers compared with the 16's here. | | My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air "blanketing" the board's bottom surface though many device edges are very close to the board's edges (.100" or less) and other design rule violations. This does not allow the "blanket" to provide the same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on "real" boards. | | I am keying on part removal success with outside T/C's attached closely to part corners to ensure I start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500 boards. Anyway, is there anyone capable of offering objective suggestions concerning this type behaviour. | | Earl Moon | | Hi Earl. I have tracked my BGA remove and replace yields since the introduction of my SRT Summit 2000 (my machine does 99 % contract BGA replacement work) With over 2000 remove-and -replaces (R-R) in 9 months my yields have never droped below 96.5 percent (reworkable). As a "job shop" I see everything under the sun for BGA rework. Here are some tips...

Check your burn pattern. Place a piece of paper under the heater core and run your profile. If your plennum is OK you will see the corners of the core get the hottest (darkest burn on the paper ). Now that you see where the heat is concintrated this can help your T/C placement strategy. Unfortunately with hot gas machines as heat is conducted through the BGA and part the perimeter areas will get hotter than the interior of the BGA. So the strategy I use is to ensure the interior perimeter balls get up to temp and unfortunately this typically means high deltas (greater than 10 deg C.) on large BGA's (352 and up). As the lesser of two evils (unsoldered joints on the interior rows vs. high temps above 210 C on the exterior rows) I always lean to ensuring all balls reflow. Invasive (destructive) profiling is the only reliable, and most accurate method of generating a thermal profile. If my customers can not supply a destructive profiling sample we do not guarantee our work and use a reliability waiver. Are you preconditioning your core? Example: Remove site one with core at room temp. Immediately remove site two with your core at a temp well above room temp . (preheated) I use conditional statements and preheat my core to 150 deg. C. Prior to allowing the core to drop over the site. This guarantees my core starts at the same temperature EVERY SITE, EVERY BOARD. (plus after the site is replaced I force the core and bottom heaters to cool down to 150 C. before homing. Also, I only allow rework to be done on boards at room tempeature. This means if board 1, site one is removed, the board must cool down to room temp before subsequent rework is performed.. This guarantees the rework is performed as I have profiled it (referenced to room temp). Yes, there is a profile difference on sites near the edge of the PCB, especially near the board clamping mechanisms (giant heat sinks) However, I have only adjusted my "zone temps" up about 30 deg. C. max to compensate. Obvously this will vary board to boad. If there is anything else I can do give me a call at 503-672-4388 I'm in-and-out all day fire-fighting on the SMT lines (just like yourself) so leave a message. P.H. Dean

reply »

Earl Moon

#12395

Re: BGA repair/rework | 6 March, 1999

| | | | I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier) using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between. | | | | Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or place and reflow two parts in sequence while the third does not budge or reflow all around the | | perimeter. | | | | This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with this phenomonon (I said something like it again)? | | | | I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing similar repairs to lesser boards - as 8 layers compared with the 16's here. | | | | My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air "blanketing" the board's bottom surface though many device edges are very close to the board's edges (.100" or less) and other design rule violations. This does not allow the "blanket" to provide the same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on "real" boards. | | | | I am keying on part removal success with outside T/C's attached closely to part corners to ensure I start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500 boards. Anyway, is there anyone capable of offering objective suggestions concerning this type behaviour. | | | | Earl Moon | | | | | Hi Earl. | I have tracked my BGA remove and replace yields since the introduction of my SRT Summit 2000 (my machine does 99 % contract BGA replacement work) With over 2000 remove-and -replaces (R-R) in 9 months my yields have never droped below 96.5 percent (reworkable). As a "job shop" I see everything under the sun for BGA rework. Here are some tips... | | Check your burn pattern. Place a piece of paper under the heater core and run your profile. If your plennum is OK you will see the corners of the core get the hottest (darkest burn on the paper ). Now that you see where the heat is concintrated this can help your T/C placement strategy. Unfortunately with hot gas machines as heat is conducted through the BGA and part the perimeter areas will get hotter than the interior of the BGA. So the strategy I use is to ensure the interior perimeter balls get up to temp and unfortunately this typically means high deltas (greater than 10 deg C.) on large BGA's (352 and up). As the lesser of two evils (unsoldered joints on the interior rows vs. high temps above 210 C on the exterior rows) I always lean to ensuring all balls reflow. | Invasive (destructive) profiling is the only reliable, and most accurate method of generating a thermal profile. If my customers can not supply a destructive profiling sample we do not guarantee our work and use a reliability waiver. | Are you preconditioning your core? Example: Remove site one with core at room temp. Immediately remove site two with your core at a temp well above room temp . (preheated) I use conditional statements and preheat my core to 150 deg. C. Prior to allowing the core to drop over the site. This guarantees my core starts at the same temperature EVERY SITE, EVERY BOARD. (plus after the site is replaced I force the core and bottom heaters to cool down to 150 C. before homing. Also, I only allow rework to be done on boards at room tempeature. This means if board 1, site one is removed, the board must cool down to room temp before subsequent rework is performed.. This guarantees the rework is performed as I have profiled it (referenced to room temp). | Yes, there is a profile difference on sites near the edge of the PCB, especially near the board clamping mechanisms (giant heat sinks) However, I have only adjusted my "zone temps" up about 30 deg. C. max to compensate. Obvously this will vary board to boad. | If there is anything else I can do give me a call at 503-672-4388 | I'm in-and-out all day fire-fighting on the SMT lines (just like yourself) so leave a message. | P.H. Dean | | PHD,

Great to see from you again. I knew you were lerking out there and would respond. This time I won't loose your email/phone stuff.

Can't thank you enough for the input, especially the burn profile. I would do more destructive (actually I would do any) if management provides approval on these very "special" boards that are being scrapped for the reasons sited. Maybe they'll see the light soon.

Speaking of SRT, what the hell is the 2000 model. Also, do you have any experience with the lower heater at 1250 watts and if so how does it affect your bottom board air "blanket" - is it more uniform.

I recognize the lower heater's capability and responsibilities, but it can have some effect on the overall profile. As I'm running the 750 watt heater, I question its affect on performance regarding those devices on the maximum edge.

I really appreciate your help, again,

Earl Moon

reply »

Dean

#12396

Re: BGA repair/rework | 6 March, 1999

| | | | | | I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier) using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between. | | | | | | Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or place and reflow two parts in sequence while the third does not budge or reflow all around the | | | perimeter. | | | | | | This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with this phenomonon (I said something like it again)? | | | | | | I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing similar repairs to lesser boards - as 8 layers compared with the 16's here. | | | | | | My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air "blanketing" the board's bottom surface though many device edges are very close to the board's edges (.100" or less) and other design rule violations. This does not allow the "blanket" to provide the same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on "real" boards. | | | | | | I am keying on part removal success with outside T/C's attached closely to part corners to ensure I start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500 boards. Anyway, is there anyone capable of offering objective suggestions concerning this type behaviour. | | | | | | Earl Moon | | | | | | | | Hi Earl. | | I have tracked my BGA remove and replace yields since the introduction of my SRT Summit 2000 (my machine does 99 % contract BGA replacement work) With over 2000 remove-and -replaces (R-R) in 9 months my yields have never droped below 96.5 percent (reworkable). As a "job shop" I see everything under the sun for BGA rework. Here are some tips... | | | | Check your burn pattern. Place a piece of paper under the heater core and run your profile. If your plennum is OK you will see the corners of the core get the hottest (darkest burn on the paper ). Now that you see where the heat is concintrated this can help your T/C placement strategy. Unfortunately with hot gas machines as heat is conducted through the BGA and part the perimeter areas will get hotter than the interior of the BGA. So the strategy I use is to ensure the interior perimeter balls get up to temp and unfortunately this typically means high deltas (greater than 10 deg C.) on large BGA's (352 and up). As the lesser of two evils (unsoldered joints on the interior rows vs. high temps above 210 C on the exterior rows) I always lean to ensuring all balls reflow. | | Invasive (destructive) profiling is the only reliable, and most accurate method of generating a thermal profile. If my customers can not supply a destructive profiling sample we do not guarantee our work and use a reliability waiver. | | Are you preconditioning your core? Example: Remove site one with core at room temp. Immediately remove site two with your core at a temp well above room temp . (preheated) I use conditional statements and preheat my core to 150 deg. C. Prior to allowing the core to drop over the site. This guarantees my core starts at the same temperature EVERY SITE, EVERY BOARD. (plus after the site is replaced I force the core and bottom heaters to cool down to 150 C. before homing. Also, I only allow rework to be done on boards at room tempeature. This means if board 1, site one is removed, the board must cool down to room temp before subsequent rework is performed.. This guarantees the rework is performed as I have profiled it (referenced to room temp). | | Yes, there is a profile difference on sites near the edge of the PCB, especially near the board clamping mechanisms (giant heat sinks) However, I have only adjusted my "zone temps" up about 30 deg. C. max to compensate. Obvously this will vary board to boad. | | If there is anything else I can do give me a call at 503-672-4388 | | I'm in-and-out all day fire-fighting on the SMT lines (just like yourself) so leave a message. | | P.H. Dean | | | | | PHD, | | Great to see from you again. I knew you were lerking out there and would respond. This time I won't loose your email/phone stuff. | | Can't thank you enough for the input, especially the burn profile. I would do more destructive (actually I would do any) if management provides approval on these very "special" boards that are being scrapped for the reasons sited. Maybe they'll see the light soon. | | Speaking of SRT, what the hell is the 2000 model. Also, do you have any experience with the lower heater at 1250 watts and if so how does it affect your bottom board air "blanket" - is it more uniform. | | I recognize the lower heater's capability and responsibilities, but it can have some effect on the overall profile. As I'm running the 750 watt heater, I question its affect on performance regarding those devices on the maximum edge. | | I really appreciate your help, again, | | Earl Moon | SRT 2000 has the following features... Solder scavenger, programable placement force up tp 3Kg., Flip chip flat mirror plus split mirror (for devices up to 48 mm), board sizes 36 X 30 inch + 9 cup holders (more than a Mercury Villager) + a host of others available.... I'm not sure how many watts are in the lower heater but the heater plennum is 18 X 24 inches. I have done boards 24 X18 X 0.150 @ 3.2 pounds My heater plennum is adjustable in the Z axis. If you need more heat maby you can move yours closer? Does your machine have "learn mode" in the software? When I am faced with a R-R and can not do a destructive profile the learn mode is a life saver. Essentially it runs your job temperatures and durations but 10 seconds prior to the end of your "spike" zone it attempts to remove the device with the pickup tube. If your guestimated thermal profile is good the device should lift off within 3 tries. However, it will continue attempting to remove the device until the maximum number of attempts is exceeded. Usually I give it 20 tries. Once the device lifts off, Bingo! At a minimum the device reached 183 deg. C. Then It (the software) will add the realized time to your job. Hence the name "learn mode". Next I will add about 30 seconds additional reflow time to ensure I am above the 183 marker (for the replacement of the device). It is very possible your heaters are inadequate for the board mass. Typically, I see about 60 to 75 % absorption of the applied energy. With such an open architechure radiation losses are great. Oh yeah, my machine software safetys are set at 450 Deg. C. on the bottom heaters. This is software selectable.. how high is your core above the BGA device. I set mine between 0.050 and 0.100 inch above the part height. I have heard of users who Kapton tape off plennum vents to dirrect the hot gas specifically to the board and or site. However, this is dangerous and SRT does not recommend it--though it has been done successfully. These boards must be something else--especially if 750 watts can not preheat the board adequately (at least 170 deg. C.) What is it a half inch thick backplane? Well if you scrap one i guess you can destructively profile that one! That will teach those pesky managers... Look foreward to hearing from you again. regards, P H Dean

reply »

Earl Moon

#12397

Re: BGA repair/rework | 7 March, 1999

| | | | | | | | I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier) using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between. | | | | | | | | Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or place and reflow two parts in sequence while the third does not budge or reflow all around the | | | | perimeter. | | | | | | | | This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with this phenomonon (I said something like it again)? | | | | | | | | I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing similar repairs to lesser boards - as 8 layers compared with the 16's here. | | | | | | | | My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air "blanketing" the board's bottom surface though many device edges are very close to the board's edges (.100" or less) and other design rule violations. This does not allow the "blanket" to provide the same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on "real" boards. | | | | | | | | I am keying on part removal success with outside T/C's attached closely to part corners to ensure I start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500 boards. Anyway, is there anyone capable of offering objective suggestions concerning this type behaviour. | | | | | | | | Earl Moon | | | | | | | | | | | Hi Earl. | | | I have tracked my BGA remove and replace yields since the introduction of my SRT Summit 2000 (my machine does 99 % contract BGA replacement work) With over 2000 remove-and -replaces (R-R) in 9 months my yields have never droped below 96.5 percent (reworkable). As a "job shop" I see everything under the sun for BGA rework. Here are some tips... | | | | | | Check your burn pattern. Place a piece of paper under the heater core and run your profile. If your plennum is OK you will see the corners of the core get the hottest (darkest burn on the paper ). Now that you see where the heat is concintrated this can help your T/C placement strategy. Unfortunately with hot gas machines as heat is conducted through the BGA and part the perimeter areas will get hotter than the interior of the BGA. So the strategy I use is to ensure the interior perimeter balls get up to temp and unfortunately this typically means high deltas (greater than 10 deg C.) on large BGA's (352 and up). As the lesser of two evils (unsoldered joints on the interior rows vs. high temps above 210 C on the exterior rows) I always lean to ensuring all balls reflow. | | | Invasive (destructive) profiling is the only reliable, and most accurate method of generating a thermal profile. If my customers can not supply a destructive profiling sample we do not guarantee our work and use a reliability waiver. | | | Are you preconditioning your core? Example: Remove site one with core at room temp. Immediately remove site two with your core at a temp well above room temp . (preheated) I use conditional statements and preheat my core to 150 deg. C. Prior to allowing the core to drop over the site. This guarantees my core starts at the same temperature EVERY SITE, EVERY BOARD. (plus after the site is replaced I force the core and bottom heaters to cool down to 150 C. before homing. Also, I only allow rework to be done on boards at room tempeature. This means if board 1, site one is removed, the board must cool down to room temp before subsequent rework is performed.. This guarantees the rework is performed as I have profiled it (referenced to room temp). | | | Yes, there is a profile difference on sites near the edge of the PCB, especially near the board clamping mechanisms (giant heat sinks) However, I have only adjusted my "zone temps" up about 30 deg. C. max to compensate. Obvously this will vary board to boad. | | | If there is anything else I can do give me a call at 503-672-4388 | | | I'm in-and-out all day fire-fighting on the SMT lines (just like yourself) so leave a message. | | | P.H. Dean | | | | | | | | PHD, | | | | Great to see from you again. I knew you were lerking out there and would respond. This time I won't loose your email/phone stuff. | | | | Can't thank you enough for the input, especially the burn profile. I would do more destructive (actually I would do any) if management provides approval on these very "special" boards that are being scrapped for the reasons sited. Maybe they'll see the light soon. | | | | Speaking of SRT, what the hell is the 2000 model. Also, do you have any experience with the lower heater at 1250 watts and if so how does it affect your bottom board air "blanket" - is it more uniform. | | | | I recognize the lower heater's capability and responsibilities, but it can have some effect on the overall profile. As I'm running the 750 watt heater, I question its affect on performance regarding those devices on the maximum edge. | | | | I really appreciate your help, again, | | | | Earl Moon | | | SRT 2000 has the following features... | Solder scavenger, programable placement force up tp 3Kg., Flip chip flat mirror plus split mirror (for devices up to 48 mm), board sizes 36 X 30 inch + 9 cup holders (more than a Mercury Villager) + a host of others available.... I'm not sure how many watts are in the lower heater but the heater plennum is 18 X 24 inches. I have done boards 24 X18 X 0.150 @ 3.2 pounds | My heater plennum is adjustable in the Z axis. If you need more heat maby you can move yours closer? | Does your machine have "learn mode" in the software? When I am faced with a R-R and can not do a destructive profile the learn mode is a life saver. Essentially it runs your job temperatures and durations but 10 seconds prior to the end of your "spike" zone it attempts to remove the device with the pickup tube. If your guestimated thermal profile is good the device should lift off within 3 tries. However, it will continue attempting to remove the device until the maximum number of attempts is exceeded. Usually I give it 20 tries. Once the device lifts off, Bingo! At a minimum the device reached 183 deg. C. Then It (the software) will add the realized time to your job. Hence the name "learn mode". Next I will add about 30 seconds additional reflow time to ensure I am above the 183 marker (for the replacement of the device). | It is very possible your heaters are inadequate for the board mass. Typically, I see about 60 to 75 % absorption of the applied energy. With such an open architechure radiation losses are great. Oh yeah, my machine software safetys are set at 450 Deg. C. on the bottom heaters. This is software selectable.. | how high is your core above the BGA device. I set mine between 0.050 and 0.100 inch above the part height. | I have heard of users who Kapton tape off plennum vents to dirrect the hot gas specifically to the board and or site. However, this is dangerous and SRT does not recommend it--though it has been done successfully. | These boards must be something else--especially if 750 watts can not preheat the board adequately (at least 170 deg. C.) What is it a half inch thick backplane? Well if you scrap one i guess you can destructively profile that one! That will teach those pesky managers... | Look foreward to hearing from you again. | regards, | P H Dean | PHD,

Thanks again for the input. Looks as if I need a 2000, or not.

We do have the older software, soon to be upgraded, but it does have the learn mode and a fine resource it is.

After your generous input, I will do more investigations concerning bottom side heating. I agree, though not always my powers to be, that this factor may be the culprit even though we get some pretty even bottom temps - not at the edge.

We max bottom temps out at 250. We do not have the benefit of using easily adjustable bottom heater adjustment. It now is positioned at about 1.5" from the board's bottom surface implying it may not matter as the hot air "blanket" may make things alright. Don't think so.

My profiles, on a most difficult 16 layer board populated with 6 BGA's of the 432 ball perimiter type, are getting closer. They are about 270 top, 250 bottom, 40 seconds reflow, and 15 additional time. Our times seem a bit out of synch with yours but the effects are very good through visual, 5D X-Ray, and electrical but only 2 out of three times.

As I may have said before, we do a remove process first to rework - what else? These profiles, gained from learn or "dummy" board profiling, provide our starting point. If the system picks up on the first or second attempt, we use this profile as the starting point for our pick and reflow sequence. Again, this works two out of three times though there are exetnuating circumstances not needing to be expressed herein.

Our rework rule states three times and you scrap. This requires making a decision after the first reflow attmept fails. We can either re-flux the BGA edges and hope it "flows" down around all affected balls to ensure reflow, or remove and replace the devices. Often, re-reflowing requires jacking up the top side heater about 20 degrees to get the stubborn balls to reflow - and not bridge the others.

And on it goes. Again, I can't thank you enough for your time. I will call you soon as others probably find this rhetoric a bit much.

Earl Moon

reply »

Steve Gregory

#12398

Re: BGA repair/rework | 7 March, 1999

| And on it goes. Again, I can't thank you enough for your time. I will call you soon as others probably find this rhetoric a bit much. | | Earl Moon | Earl and Dean,

No,no,no...please continue here. I've been gratefully reading everything you two have been exchanging with great interest! This is good stuff! Not only to further my feeble knowledge, but to use (if you don't mind) as a very good technical argument for those "pesky management types" in illustrating that having a handheld Hakko unit is really not to be considered as a viable tool in todays world of BGA R & R...no matter how resourceful one can be. As you may have observed lately by my posts here and elsewhere, I need all the help I can get...I feel like I'm on a sinking ship...

Looking forward to more...

-Steve Gregory-

reply »

Earl Moon

#12399

Re: BGA repair/rework | 8 March, 1999

| | | And on it goes. Again, I can't thank you enough for your time. I will call you soon as others probably find this rhetoric a bit much. | | | | Earl Moon | | | Earl and Dean, | | No,no,no...please continue here. I've been gratefully reading everything you two have been exchanging with great interest! This is good stuff! Not only to further my feeble knowledge, but to use (if you don't mind) as a very good technical argument for those "pesky management types" in illustrating that having a handheld Hakko unit is really not to be considered as a viable tool in todays world of BGA R & R...no matter how resourceful one can be. As you may have observed lately by my posts here and elsewhere, I need all the help I can get...I feel like I'm on a sinking ship... | | Looking forward to more... | | -Steve Gregory- | Steve,

I remember your earlier dilemma concerning rework/repair while considering a less than optimal system. I know PHD can back this up when I say, no matter how resourceful one is, it's the next thing to impossible using anything less than a programmable, computerized system with serious operatior interactive capabilities. It sometimes seems impossible to use one of these semi-auto beasts to get the job done especially in light of our 16-30 layer MLB's that are classified all the way from one through nine at this operation.

You simply must have the ability to learn a profile from a remove sequence. At least that's often where I have to start. Then, I apply this profile (as long as it's in the 150, 183, and liquidous windows) for reflow (keying mostly on the 183 window when the hot T/C goes high or out of liquidous and the delta exceeds 20 degrees or so because the MLB's internal thermal mass). Also, the dummy thermocouple profiles aid as a guideline to start a place and reflow sequence when no first articles are immediately available as with Dean.

Of course, as Dean says, I have plenty of them left over after not succeeding with the process. However, there are other issues for me concerning scrap as we have traces running too close to BGA pads requiring "touch-up" to "prevent" bridging because the solder mask doesn't cover the damn area the designers did not consider. Often the touch-up doesn't get the job done.

Yes, I really wish you the best in your battle to get a system that will be more operator friendly, while doing the job of course, than requiring all your time. Simply running one sequence often takes 20 - 30 minutes including setup, warmup, selecting sequence, alignment, start, equalization time, soak time, reflow time, cool down, and visual inspection not withstanding our time in X-Ray and follow up electrical test.

By the way, our X-Ray (all 8000 lbs of it) often saves our butts. However it has limitations as it is not possible to see all shorts directly under the balls, if they exist. It does an excellent job using acceptance rules as insufficient or excess solder, solder balls, bridging, etc.

Alignment issues are not so critical on most any system, but thermal (top and bottom heater settings) certainly are. Without a serious system, I just don't see how it can be done. There are just too many variables for an operator to contend with even with an automated system.

From an engineering standpoint, I don't want to spend eight hours a day doing what is supposed to be done by our highly talented, well trained operators. When an automated systems is properly setup, with all the variables considered (board and device type, rework sequence to be performed, machine setup, alignment, thermal profiles, etc., the job runs smoothly. When not, it is not always pleasant.

And on it goes with so much more to say and do,

Earl Moon

reply »

Sherry_Warner

#12400

Re: BGA repair/rework | 8 March, 1999

I couldn't agree with Steve more! Please don't stop ....

I can use all the help and tips focusing around BGA rework especially using the SRT 1000 station. Doesn't get any better than this :-)

Thanks!!

-Sherry

reply »

Steve Gregory

#12401

Re: BGA repair/rework | 8 March, 1999

Earl wrote:

>> Alignment issues are not so critical on most any system, but thermal >>(top and bottom heater settings) certainly are. Without a serious >>system, I just don't see how it can be done.

Thanks again Earl for your valuable communications..

You're comment above leads me to a question I have asked earlier about a Pace system, maybe Dean or anybody else might have a few comments about the new Therma-flow TF-700 system. It has a integrated bottomside preheater that I believe is capable of 700 watts, and the the primary heat source for the nozzle is 1000 watts. So it does seem "beefy" enough going by your discussions...whatcha' think?

-Steve-

reply »

Earl Moon

#12402

Re: BGA repair/rework | 8 March, 1999

| Earl wrote: | | >> Alignment issues are not so critical on most any system, but thermal >>(top and bottom heater settings) certainly are. Without a serious >>system, I just don't see how it can be done. | | Thanks again Earl for your valuable communications.. | | You're comment above leads me to a question I have asked earlier about a Pace system, maybe Dean or anybody else might have a few comments about the new Therma-flow TF-700 system. It has a integrated bottomside preheater that I believe is capable of 700 watts, and the the primary heat source for the nozzle is 1000 watts. So it does seem "beefy" enough going by your discussions...whatcha' think? | | -Steve- | | Steve,

My reply may show up. If not, I will reconstruct it later. It was a thing of beauty appreciated by all who would dare read it - eight or nine words, or was it paragraphs. Anyway, I know if anyone can fly by the seat of his/her pants, you can.

If the message shows up somehow, you will be so much more informed concerning why I just can't use stuff unless its computer integrated. My problem - not yours.

If it doesn't show up, just remember keep your EQ and soak times at about 100 seconds, your time in the 183 C. box from 60 to 100 seconds, your time between entering and leaving 205 not more than 45 seconds, additional reflow time at about 25 seconds, and all the rest looking like top at 275, bottom at 250, reflow at 45, additional at 15 plus and learn from your remove sequence.

If your machine can do all that and all that I lost over the past hour, buy your future X rework machine and teach us all how to do it without computer intervention.

For PHD, with your help I dialed it in and had much sucess today. Tomorrow is another day but am much more hopeful.

I'm really sorry about my stupid human trick of not backing up what I sent to the forum. Is it lost forever?

Regards and more,

Earl Moon

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Michael Larsen

#12403

Re: BGA repair/rework | 8 March, 1999

| | I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier) using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between. | | Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or place and reflow two parts in sequence while the third does not budge or reflow all around the | perimeter. | | This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with this phenomonon (I said something like it again)? | | I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing similar repairs to lesser boards - as 8 layers compared with the 16's here. | | My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air "blanketing" the board's bottom surface though many device edges are very close to the board's edges (.100" or less) and other design rule violations. This does not allow the "blanket" to provide the same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on "real" boards. | | I am keying on part removal success with outside T/C's attached closely to part corners to ensure I start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500 boards. Anyway, is there anyone capable of offering objective suggestions concerning this type behaviour. | | Earl Moon |

First off, I have used both the SRT 1000 and 2000 and have seen unsatisfactory results with both. They are both extremely inconsistent and have shown delta T's of over 20 degrees on the same board, same profile, different day. I even thermocoupled the bottom heater plate and saw that it carries a delta T of over 80 degrees from the middle to about 4 inches diagonally from the corner. We have since purchased Air-Vac rework stations and have been much more satisfied. The Air-Vac is triggered off of board temperature to go to the next step in the profile. The SRT's trigger off of time which can be a problem if the machine and board are both not at room temp when the profile is started.

Equipment aside, on many of the complex boards and components (boards up to 24 layers and .120" thick and 664 BGAs) I have found that using a long preheat and soak with only the bottom heater plate will help. This gets the component and board nice and toasty before bringing down the core when using the SRT. It will also help to bring the delta T across the component and board down to more reasonable numbers. Try creating a profile board with TCs at all four corners (actually a couple of rows in) and run the board under different situations. I.E. board at room temp, board preheated, machine start from cold, machine hot, etc. and note the results.

And just for fun, run the profile with board and the machine starting at room temp for about 10 days, maybe even twice per day and record the peak temp. You will probably see a large swing in the performance of the machine.

Good luck,

Mike Larsen

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Dean

#12404

Re: BGA repair/rework | 8 March, 1999

| | Earl wrote: | | | | >> Alignment issues are not so critical on most any system, but thermal >>(top and bottom heater settings) certainly are. Without a serious >>system, I just don't see how it can be done. | | | | Thanks again Earl for your valuable communications.. | | | | You're comment above leads me to a question I have asked earlier about a Pace system, maybe Dean or anybody else might have a few comments about the new Therma-flow TF-700 system. It has a integrated bottomside preheater that I believe is capable of 700 watts, and the the primary heat source for the nozzle is 1000 watts. So it does seem "beefy" enough going by your discussions...whatcha' think? | | | | -Steve- | | | | | Steve, | | My reply may show up. If not, I will reconstruct it later. It was a thing of beauty appreciated by all who would dare read it - eight or nine words, or was it paragraphs. Anyway, I know if anyone can fly by the seat of his/her pants, you can. | | If the message shows up somehow, you will be so much more informed concerning why I just can't use stuff unless its computer integrated. My problem - not yours. | | If it doesn't show up, just remember keep your EQ and soak times at about 100 seconds, your time in the 183 C. box from 60 to 100 seconds, your time between entering and leaving 205 not more than 45 seconds, additional reflow time at about 25 seconds, and all the rest looking like top at 275, bottom at 250, reflow at 45, additional at 15 plus and learn from your remove sequence. | | If your machine can do all that and all that I lost over the past hour, buy your future X rework machine and teach us all how to do it without computer intervention. | | For PHD, with your help I dialed it in and had much sucess today. Tomorrow is another day but am much more hopeful. | | I'm really sorry about my stupid human trick of not backing up what I sent to the forum. Is it lost forever? | | Regards and more, | | Earl Moon | In our business ROBUST, REPEATABLE process rules the land. Unfortunately, it takes time to characterize and familiarize ourselves with the new equipment. ( Meanwhile, while us techs are un-crating the equipment the sales staff hs booked 1000 units due in one week!) The point is every day I learn something new on equipment I thought I was "old hat" with. If given a choice between a manufacturing environment governed by low automation (technology) / high "craftsmanship" (operators) vs. high automation (technology) / low "craftsmanship" (operators) the latter is much more controllable and predictable in a given system. Best of rework to all, Dean

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