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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


bob

#15990

FR4 vs Ceramic mismatch | 5 May, 1998

I hear that there is a problem with using ceramic parts that are sizeable. Apparently, there is a mismatch in the Temperature Coefficient of Expansion between the FR4 and ceramic materials which causes the soldered erminations to weaken and eventually fracture. True? Someone mentioned a paper that was written some time ago ...

reply »

justin medernach

#15991

Re: FR4 vs Ceramic mismatch | 6 May, 1998

| I hear that there is a problem with using ceramic parts that are sizeable. Apparently, there is a mismatch in the Temperature Coefficient of Expansion between the FR4 and ceramic materials which causes the soldered erminations to weaken and eventually fracture. True? Someone mentioned a paper that was written some time ago ... Bob, I'm back. Yes, there is a thermal mismatch. Will it cause a fractured solder joint? Eventually. FR4 expands and contracts with a much greater amplitude than ceramic. Therefor, the solder joint will be stressed, after multiple thermal excursions, and will eventually fracture. The issue here is how long it will take. What is the functionality of your product? Will the device see multiple thermal cycles? What is the expected life cycle of the product? Is it high reliability or "radio shack consumer electronics?" These are questions you need to ask yourself prior to incorporating these things in a design. From a process standpoint, you need to minimize the amount of times the substrate will see reflow temperatures. These cycles, between ambient and 225 C, are very stressful to the assembly. Remember, this includes rework operation so have a solid and controlled process. Regards, Justin Medernach

reply »

Earl Moon

#15992

Re: FR4 vs Ceramic mismatch | 15 May, 1998

| | I hear that there is a problem with using ceramic parts that are sizeable. Apparently, there is a mismatch in the Temperature Coefficient of Expansion between the FR4 and ceramic materials which causes the soldered erminations to weaken and eventually fracture. True? Someone mentioned a paper that was written some time ago ... | Bob, | I'm back. Yes, there is a thermal mismatch. Will it cause a fractured solder joint? Eventually. FR4 expands and contracts with a much greater amplitude than ceramic. Therefor, the solder joint will be stressed, after multiple thermal excursions, and will eventually fracture. The issue here is how long it will take. What is the functionality of your product? Will the device see multiple thermal cycles? What is the expected life cycle of the product? Is it high reliability or "radio shack consumer electronics?" These are questions you need to ask yourself prior to incorporating these things in a design. | From a process standpoint, you need to minimize the amount of times the substrate will see reflow temperatures. These cycles, between ambient and 225 C, are very stressful to the assembly. Remember, this includes rework operation so have a solid and controlled process. | Regards, | Justin Medernach Problems always exist between ceramic, expanding at 5-7 ppm, when attached to substrates expanding at 15-17 ppm or more. Also, copper conductive surfaces expand at 17-19 ppm. To overcome this in military/aerospace applications we used TCE matching materials as Kevlar and CIC tailoring cores in MLB's. As these methods are not practical in commercial applications, we do other things to minimize mismatch causing defects during both soldering and operational thermal excursions. However, if you are not using LCCC device types (only chip devices) you may minimize risk in several ways. I will be glad to help you more if you wish to email me off forum. Sincerely, Earl Moon

reply »

 Reflow System

ii-feed SMD Intelligent Feeder