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

Printed Circuit Board Assembly & PCB Design Forum

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PCB Thermal shock



PCB Thermal shock | 3 November, 2001

Hi Could somesomeone help to let me know can bare PCB (FR4) is damaged by thermal shock? Can difference of CTE from copper or solder to FR4 damage PCB from apply heat too fast? Any specification or standard can i refer? Thank you


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PCB Thermal shock | 5 November, 2001

What�s the problem?

There area many heat related failure mechanisms in bare boards. You can damage boards with heat several ways. A couple favorites [Don�t try this at home. Perform on a closed track by professional solders only.] are: * Put a heated soldering iron on a pad for about 30 seconds. * Put a board on the rocks [ice] for a couple hours and then run it over the wave/reflow. * Put a board in a bucket of water overnight, dry it off, and then run it over the wave/reflow. * Put the conveyor in 4th gear, put a board on the conveyor, and then run it over the wave/reflow.

Your FR-4 board is fabricated from layers of: * Copper * Epoxy * Woven fiberglass

Each succeeding layer has different properties [ie, CTE, tg, etc.].

Solder Float Test: * J-STD-003 After fluxing and draining per . . . slide the coupon gently on molten solder. Allow coupon to float on solder for 5 seconds maximum. The coupon may be depressed into the solder bath to a maximum of 50% of the coupon thickness after it has been initially floated on the solder. After the elapsed time, slide the coupon off molten solder. Hold coupon still and horizontal until solder solidifies. * J-STD-003 section 3.5.1 The bulk temperature of the solder bath shall be maintained at 245�C + 5�C [473�F + 9�F] unless another temperature is agreed to by the vendor and user.

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