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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Reflow Profiling Question

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Reflow Profiling Question | 21 December, 2007

Hello All, I read AIMs article "Time Above Liquidus". It was very informative and a good read. One thing that the article didn't touch on, that is a mystery to me, is thermal shock to components during the ramp up stage of a profile. If you want to try and achieve 2-3 degrees/sec rampup rate sometimes you need a relatively high temperature at the onset of the profile. I notice on my profiles that a Zone1 temp of 150c will yield about 1-1.5 degrees/sec ramp up on most assemblies. Sometimes lower around .8. My question: 1. Is there a temperature that should not be exceeded at the onset of a profile due to risk of damaging components with thermal shock? 2. If I was running a tin/lead solder on a regular .6inch thick assembly and I have a Zone1 temp of 215c or higher to achieve 2-3degrees/sec on the largest component, would that possibly shock the smaller components on the assembly? When profiling I always gauge the profile from the largest/most critical component on the assembly. ie:BGAs, QFPs. Considering the thermal mass of these components is much higher than smaller components, the smaller components are going to be subject to much higher temps, for longer periods of time and at much higher slope rates. Do you guys/gals have any information/links on this issue? Thanks!!!!

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Reflow Profiling Question | 21 December, 2007


Think "opposite". You actually want to MINIMIZE the ramp-up rate. Think about 2 - 3�C per second as your upper limit for ramp up. You don't want to go more than 4�C per second for thermal shock reasons.

All of this, of course, depends on type of oven, # of zones, thermal mass of your board, etc. That's where profiling comes in. :-)

The trend seems to be.... nobody wants to do profiles any more!

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Reflow Profiling Question | 22 December, 2007

My understanding is that if the delta T was 4deg/sec then chip capacitors would delaminate. I have no evidence to support this just an engineers advice.


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Reflow Profiling Question | 26 December, 2007

Hey Andy, Thought you were buying a line?

Do some homework, bro. This is manufacturing...not building a crystal set to listen to a.m. radio...

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Reflow Profiling Question | 26 December, 2007

Delta T is the temparture different between the highest and lowest measured point on a profile. Ramp and cooling rate should not exceed 4deg c/sec to prevent thermal shock to the components and pcbs. This will also minimise delamination.

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