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Pallet absorb thermal heat : compensate by higher deg-C?

ianchan

#6811

Pallet absorb thermal heat : compensate by higher deg-C? | 9 June, 2001

Hi Folks,

My Production runs a uBGA-liken product, and uses Pallets to support the 0.8mm thick pcb, during the SMT + reflow oven process.

Process/QA see occurs: 1) 0402 unsolder? 2) 0402 tombstone? 3) "uBGA" poor-visual joints (dry joints)?

Took a thermal profile, all process parameter maintained the same : (A) x1 pcba with Pallet support, (B) x1 pcba (same) without Pallet support.

Findings: 1) dipping of profile occurs in (A), 2) Oven zone : heat-transfer problem in (A), 3) non-uniform RAMP rate in (A), 4) heat (energy) dissipation in (A), 5) peak-temperature : (B)-(A)= +10 deg-C difference

Question : 1) To offset the heat-absorb ability of the Pallet, that artifically lowers my pcba temperature, is it advisable to artifically increase the overall, oven zone temperatures? 1b) estimate by +10 deg-C each zone?

2) If decide not to uniform overall increase each oven zone, any ideas how to accurately measure the Pallet heat-absorb rates, during each stage of the oven zone travel?

3) Note : Pallet material is "durapol IGM L 100"?

4) Anyone has experience in Pallet absorption issues, that lowered the overall oven zone temperatures, that resulted in : a) unsolder? b) tombstone? c) uncooked (dry) solder joint?

Appreciate any feedback.

Regards, ianchan 09 june 2001

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#6813

Pallet absorb thermal heat : compensate by higher deg-C? | 9 June, 2001

Yes, your pallet will absorb / steal heat.

It sounds like you are doing a good job in understanding the issues. Yes, the pallet could be the problem. Is this a new run that you are starting? Or has everything been OK, but recently you've begun to see this problem?

Consider attaching a thermocouple to the board at your pads with problems and developing your profile based on the temperature of those pads.

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#6818

Pallet absorb thermal heat : compensate by higher deg-C? | 10 June, 2001

Is this a Convection Oven or IR? If convection, you can increase the air velocity in the zones if the oven has this ability. You should do as Dave has explained. If you must use pallets when reflowing your components, you need to profile in the same manor as you will be producing. As Dave has suggested, place a thermocouple in the area you are having problems with and also in areas where you are not. Your profile should be made utilizing the paste manufacturers specs. You should be able to get the parts that you are having problems with up to the required temps to reflow properly, however, watch for the other components that are now ok as they may get hotter than they should.

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ianchan

#6821

Pallet absorb thermal heat : compensate by higher deg-C? | 10 June, 2001

Hi Guys,

Thanks for the tips, will try it on next run.

Regards, ianchan :)

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Rob Fischer

#6835

Pallet absorb thermal heat : compensate by higher deg-C? | 12 June, 2001

I assume the material you are using is black. This may sound far fetched but try using a lighter color material. Going from black to gray has given users as much as fifteen degrees F. less in heat loss.

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CPI

#6837

Pallet absorb thermal heat : compensate by higher deg-C? | 12 June, 2001

Rob: Wouldn't that only apply to IR ovens. If using a true convection oven the color of the material wouldn't hinder output at all "Right". Don�t want to see someone spend money on new tooling if unnecessary.

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ianchan

#6842

Pallet absorb thermal heat : compensate by higher deg-C? | 12 June, 2001

Hi mates,

thanks for the interest on this topic, just to share info to clarify any queries :

1) am using light blue-grey materials for the Pallet 2) am using Hot Air Convection Reflow Oven

3) I suspect its due to the Pallet materials properties, that dissipates heat so fast, and believe the colour doesn't have major impact?

4) Am still scratching heads, as to how to measure the heat absorb levels by the Pallet, during reflow stage?

5) Based on previous experiment, find peak temperature between : A) PCBA board without Pallet use (A) & B) PCBA with Pallet use (B), demostrates a thermal difference of (A)-(B)= +10deg-C

6) Any further comments, appreciated :)

Regards, ianchan 13 june 2001

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ianchan

#6844

Pallet absorb thermal heat : compensate by higher deg-C? | 12 June, 2001

Hi mates,

actually my whole problem, is whether to :

1) To offset the heat-absorb ability of the Pallet, that artifically lowers my pcba temperature, is it advisable to artifically increase the overall, oven zone temperatures? offset by estimated +10 deg-C each zone?

2) If decide not to uniform overall increase each oven zone, any ideas how to accurately measure the Pallet heat-absorb rates, during each stage of the oven zone travel? so that I can increase accurately each individual oven zone thermal setting?

3) Can not increase oven zone temperature settings individual, unless I can measure and determine each zone heat loss, a thermal loss absorb by the Pallet.

4) This thermal loss, artifically lowers my actual heat level & distribution across the PCBA during reflow, and results in reject (headaches) modes :

4a) tombstone 4b) unsolder

Anyone has good "aspirin/panadol" to recommend?

Thanks, and Regards, Ian Chan / QA 13 june 2001

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#6875

Pallet absorb thermal heat : compensate by higher deg-C? | 14 June, 2001

Ian,

It appears to me you are trying to reflow the star wars project. All this talk about thermal absorbtion, heat differential, etc., it' only a reflow profile? If you read back over the suggestions of all other memos, you will find the solution.

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ianchan

#6876

Pallet absorb thermal heat : compensate by higher deg-C? | 14 June, 2001

Hi mate,

thanks for the "starwars project" irk, it sort of sets my rump on track to "lah-lah-land", i need help here, coz this fric'kin pcba, is going onto a control panel, for a governmental fighter jet,

ianchan / QA 14 june 2001

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#6887

Pallet absorb thermal heat : compensate by higher deg-C? | 14 June, 2001

I must be missing something.....why can't you simply attach thermocouples, profile the assembly, and adjust your zones as required to reach the parameters required by your paste and component specifications? Is there a restriction on that process for military applications? I'm not saying you don't have a reason, I just don't understand what it is.

Regards,

Steve

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