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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Stoney Tsai

#14888

DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 23 July, 1998

Hi, We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. Any good suggestion would be highly appreciated! Stoney Tsai

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Frank J. de Klein

#14890

Re: DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 24 July, 1998

| Hi, | We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. | Any good suggestion would be highly appreciated! | Stoney Tsai ***************************** Dear Stoney, The PLCC84 will fall down due to the fact that the component weight divided by the surface area of solder (liquidious) which is trying to hold the the component to the board, exceeds the 50 mg/mm2 limit which is generally accepted as the maximum weight/mm2 which can still be held by the solder provided that the conveyor runs without vibrations and that the board is properly supported to avoid excessive sagging. Changing the profile will not help you much as you will not be able to reach a sufficiently large temperature differential between the top and the bottomside of the board. Regards, Frank J. de Klein

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Justin Medernach

#14893

Re: DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 24 July, 1998

| | Hi, | | We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. | | Any good suggestion would be highly appreciated! | | Stoney Tsai | ***************************** | Dear Stoney, | The PLCC84 will fall down due to the fact that the | component weight divided by the surface area of | solder (liquidious) which is trying to hold the | the component to the board, exceeds the 50 mg/mm2 | limit which is generally accepted as the maximum | weight/mm2 which can still be held by the solder | provided that the conveyor runs without vibrations | and that the board is properly supported to avoid | excessive sagging. | Changing the profile will not help you much as you | will not be able to reach a sufficiently large | temperature differential between the top and the | bottomside of the board. | Regards, | Frank J. de Klein Stoney, Frank is correct. The package is too heavy. Here are some things you might try. Hit the location with a dab of epoxy if you have in-line adhesive dispense. Also, look at your convection in the reflow zones. Try to drop the air amplifiers to a minimum and reprofile your product. You may be able to get it. I suspect that you are "up the creek" though. Regards, Justin Medernach

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Dave F

#14891

Can We Check Our Units?? | 24 July, 1998

| | Hi, | | We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. | | Any good suggestion would be highly appreciated! | | Stoney Tsai | ***************************** | Dear Stoney, | The PLCC84 will fall down due to the fact that the | component weight divided by the surface area of | solder (liquidious) which is trying to hold the | the component to the board, exceeds the 50 mg/mm2 | limit which is generally accepted as the maximum | weight/mm2 which can still be held by the solder | provided that the conveyor runs without vibrations | and that the board is properly supported to avoid | excessive sagging. | Changing the profile will not help you much as you | will not be able to reach a sufficiently large | temperature differential between the top and the | bottomside of the board. | Regards, | Frank J. de Klein Frank: I agree with you, except on the unit of measure. I think it should be gm per in2 rather than gm per mm2. Dave F

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Steve Gregory

#14895

Re: DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 24 July, 1998

Stoney, One thing you might do before you start dispensing epoxy, (...I know this might be a bit of a pain) is to run your boards on the mesh belt instead of the edge-rail conveyer. I used to have to do that with some very,very dense double sided memory modules due to the sheer weight of all the DRAM. If I got the profile hot enough to reflow, I'd be bowing my boards and parts would start dropping, if I cooled it up a bit to keep from bowing, I'd have cold solder...so I just ran em' on the mesh belt. Make sure your mesh belt is traveling smoothly and there ain't no "whoop-dee-do's" through-out the boards travel thru the oven...(make sure your belt is, and stays, nice and flat) -Steve Gregory-

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Bob Willis

#14896

Re: DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 24 July, 1998

Sorry guys have a look at this list of component weights and then work out the surface area of the lead/pad and then come back on the PLCC issue. Chip 0805���� 0.007g������ 2 Chip 1206���� 0.009g���� 2 Chip 1210���� 0.012g���� 2 SOT23���������0.008g���� 3 SOT89���������0.0976g���� 4 V/Resistor���� 0.124g���� 3 MELF�����������0.1325g���� 2 Mini MELF���� 0.031g�������� 2 SOIC8����������0.102g 8 SOIC12�������� 0.123g 12 SOIC16�������� 0.142g 16 TSOP20�������� 0.212g 20 PLCC28�������� 0.688g 28 PLCC44�������� 2.21g 44 PLCC68�������� 4.67g 68 PLCC100�������� 9.97g 100 LCCC44�������� 5.32g 44 PLCC84�������� 5.21g 84 PLCC100�������� 9.97g 100 QFP100�������� 4.24g 100 BGA225�������� 2.65g 225 BGA313�������� 6.32g 313 CBGA256�������� 24.21g 256 CCGA625�������� 29.53g 625 CCGA1089����� 34.12g 1089 Tape BGA360���� 2.695g 360 The formula that most people use is conservitive. The real problem for double sided reflow is board sag and vibration. If you want a copy of the Double Sided Reflow Desing and Assembly report contact the main USA SMTA office. The proceeds from the sale of the report is going to a USA charity.

| Stoney, | One thing you might do before you start dispensing epoxy, (...I know this might be a bit of a pain) is to run your boards on the mesh belt instead of the edge-rail conveyer. I used to have to do that with some very,very dense double sided memory modules due to the sheer weight of all the DRAM. If I got the profile hot enough to reflow, I'd be bowing my boards and parts would start dropping, if I cooled it up a bit to keep from bowing, I'd have cold solder...so I just ran em' on the mesh belt. Make sure your mesh belt is traveling smoothly and there ain't no "whoop-dee-do's" through-out the boards travel thru the oven...(make sure your belt is, and stays, nice and flat) | -Steve Gregory-

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Phillip Hunter

#14894

Re: DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 25 July, 1998

Use caution if epoxy is dispensed under the PLCC 84. If the "SMT Gods" look unfavorably onto you rework will be difficult. I had a ceramic PLCC 84 which weighed 15 grams (MCM) and due to packaging failures (glass seal to metal cover) rework was the norm. Anyways rather than using epoxy under the part Epoxy was "briged" up from from the PCB to the IC's oposing corners. I even experimented with water solouble adhesives. However, outgassing was a problem and affected the solder. Good luck! | | | Hi, | | | We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. | | | Any good suggestion would be highly appreciated! | | | Stoney Tsai | | ***************************** | | Dear Stoney, | | The PLCC84 will fall down due to the fact that the | | component weight divided by the surface area of | | solder (liquidious) which is trying to hold the | | the component to the board, exceeds the 50 mg/mm2 | | limit which is generally accepted as the maximum | | weight/mm2 which can still be held by the solder | | provided that the conveyor runs without vibrations | | and that the board is properly supported to avoid | | excessive sagging. | | Changing the profile will not help you much as you | | will not be able to reach a sufficiently large | | temperature differential between the top and the | | bottomside of the board. | | Regards, | | Frank J. de Klein | Stoney, | Frank is correct. The package is too heavy. Here are some things you might try. Hit the location with a dab of epoxy if you have in-line adhesive dispense. Also, look at your convection in the reflow zones. Try to drop the air amplifiers to a minimum and reprofile your product. You may be able to get it. I suspect that you are "up the creek" though. | Regards, | Justin Medernach

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Stoney Tsai

#14889

Re: DOUBLE REFLOW WITH HEAVY WEIGHT PLCC PACKAGE | 25 July, 1998

| Hi, | We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. | Any good suggestion would be highly appreciated! | Stoney Tsai ********************** Thx for all of your introductions, I would get a try! Thx again! Stoney Tsai

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Frank J. de Klein

#14892

Re: Can We Check Our Units?? | 27 July, 1998

Dear Dave, Sure we can ! There are two values going around. One is 50 mg/mm2 The other one is 30 g/inch2 (30 * 1000) / (25.4 * 25.4) = 46.5 mg/mm2 So we are talking the same language. Regards, Frank J. de Klein | | | Hi, | | | We have encountered one serious problem that heavy packages falling down during second side reflow, especially for PLCC 84. I believe it caused by temperature profile setting. | | | Any good suggestion would be highly appreciated! | | | Stoney Tsai | | ***************************** | | Dear Stoney, | | The PLCC84 will fall down due to the fact that the | | component weight divided by the surface area of | | solder (liquidious) which is trying to hold the | | the component to the board, exceeds the 50 mg/mm2 | | limit which is generally accepted as the maximum | | weight/mm2 which can still be held by the solder | | provided that the conveyor runs without vibrations | | and that the board is properly supported to avoid | | excessive sagging. | | Changing the profile will not help you much as you | | will not be able to reach a sufficiently large | | temperature differential between the top and the | | bottomside of the board. | | Regards, | | Frank J. de Klein | Frank: I agree with you, except on the unit of measure. I think it should be gm per in2 rather than gm per mm2. Dave F

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