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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Tom Gervascio

#16944

Rework induced thermal shock of SMD capacitors | 30 December, 1997

Has anyone had any experience with thermal shocking and cracking of SMD capacitors during the rework process? My company was advised to preheat capacitors to 125 C at a rate of 2 C/sec before replacing them onto boards. Would this maybe degrade component solderability if done over and over again? Is anyone else doing special precautions and methods?

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justin medernach

#16951

Re: Rework induced thermal shock of SMD capacitors | 31 December, 1997

| Has anyone had any experience with thermal shocking | and cracking of SMD capacitors during the rework process? | My company was advised to preheat capacitors to 125 C | at a rate of 2 C/sec before replacing them onto boards. | Would this maybe degrade component solderability | if done over and over again? Is anyone else doing special precautions and methods? Tom, Any time you send a metalized component through a thermal cycle you will catalyze the oxidation process and thereby reduce solderability. Your irons may be too hot if you are cracking caps during the rework process. We have never done any preheating of components or substrates during the rework process you are describing and have not seen the issue you are refering to. Have you had this problem yet or is it just a concern? Best Regards, justin medernach flextronics int'l

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Ken Daniels

#16950

Re: Rework induced thermal shock of SMD capacitors | 31 December, 1997

| Has anyone had any experience with thermal shocking | and cracking of SMD capacitors during the rework process? | My company was advised to preheat capacitors to 125 C | at a rate of 2 C/sec before replacing them onto boards. | Would this maybe degrade component solderability | if done over and over again? Is anyone else doing special precautions and methods?

I have twice experienced problems similar to those you describe. The causes were not related. Once there was a thermal issue and was solved with 600 degree F fixed temp irons. 500 F is available as well. The other problem was the result of degraded components. For whatever reason, a particular lot of capacitors had a tendency to fracture rather easily. We performed a comparative stress test against a non-problematic component.

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Scott McKee

#16949

Re: Rework induced thermal shock of SMD capacitors | 31 December, 1997

| Has anyone had any experience with thermal shocking | and cracking of SMD capacitors during the rework process? | My company was advised to preheat capacitors to 125 C | at a rate of 2 C/sec before replacing them onto boards. | Would this maybe degrade component solderability | if done over and over again? Is anyone else doing special precautions and methods? I've ran across several components you've described. I do work for JPL and they insist that ALL ceramic SMT capacitors be reflowed, not hand soldered. I have another company who has an EMI filter that insists on reflow -- their recommended rework is to us an iron that does not exceed 280 degrees C, do not expose the device to heat for over 10 Seconds (cumulative) and to not touch the device with the iron tip. If you follow these instructions, you should be ok. Keep in mind, most soldering irons run from 700-900 degree F, much too hot to use. Good Luck, Scott

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scott cook

#16948

Re: Rework induced thermal shock of SMD capacitors | 1 January, 1998

| Has anyone had any experience with thermal shocking | and cracking of SMD capacitors during the rework process? | My company was advised to preheat capacitors to 125 C | at a rate of 2 C/sec before replacing them onto boards. | Would this maybe degrade component solderability | if done over and over again? Is anyone else doing special precautions and methods? Tom, Have you investigated hot air pencils? You can shield surrounding areas with kapton tape, and reflow the joints safely.....try one, and use a thermal profiler to set up your dwell times...... BTW, Good to see you on-line, ya big lug! scott

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David Jacks

#16947

Re: Rework induced thermal shock of SMD capacitors | 3 January, 1998

Tom: You are right. Pre-heating is just as necessary in rework as it is in intiial production. Zephyrtronics produces an economical convective bottom side pre-heater known as an airbath. This product ramps the substrate and assembly at 2-4 degrees C per second and is fully temperature controlled. When used with a hot air pencil, you can remove and replace SMD capacitors all day long with ease and without worry of thermal shock. This product was awarded the 1996 Vision Award at the Surface Mount Expo in Silicon Valley for Best New Product of the Year for Rework. Please visit the web site at www.zeph.com for more information. Best Regards, David Jacks

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Bob Willis

#16946

Re: Rework induced thermal shock of SMD capacitors | 11 January, 1998

Most componnent cracking is mechanicaly produced a guide to causes of capacitor damage is included as a download file on my web page www.bobwillis.co.uk I feel that the supplier is looking to blame some one else. IPC make comment on pre heating chip parts in thire video on rework and process I feel unecessary. | Has anyone had any experience with thermal shocking | and cracking of SMD capacitors during the rework process? | My company was advised to preheat capacitors to 125 C | at a rate of 2 C/sec before replacing them onto boards. | Would this maybe degrade component solderability | if done over and over again? Is anyone else doing special precautions and methods?

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Bob Willis

#16945

Re: Rework induced thermal shock of SMD capacitors | 11 January, 1998

Most componnent cracking is mechanicaly produced a guide to causes of capacitor damage is included as a download file on my web page www.bobwillis.co.uk I feel that the supplier is looking to blame some one else. IPC make comment on pre heating chip parts in thire video on rework and process I feel unecessary. | Has anyone had any experience with thermal shocking | and cracking of SMD capacitors during the rework process? | My company was advised to preheat capacitors to 125 C | at a rate of 2 C/sec before replacing them onto boards. | Would this maybe degrade component solderability | if done over and over again? Is anyone else doing special precautions and methods?

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