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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Chiakl

#15257

TCE for Ais | 25 June, 1998

Hi there, Does any one know what is TCE for fully wet saturated FR4. I came to know that for Dry FR4 the TCE is about 15-19 PPM �C. Is that true?

Appreciated for your help. rgs, chiakl

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Steve A

#15258

Re: TCE for Ais | 25 June, 1998

| Hi there, | Does any one know what is TCE for fully wet saturated FR4. I came to know that for Dry FR4 the TCE is about 15-19 PPM �C. Is that true? | | Appreciated for your help. | rgs, | chiakl Chiakl, It looks like you are speaking of what could also be termed as "Coefficient of Thermal Expansion (CTE). This is commonly expressed in cm /(cm * C) or dimensional change per degree of temperature change. One of my sources of information states that FR4 is in fact 16. My guess is that FR4 was engineered to match the CTE of copper. I am not aware of any studies of CTE reguarding moisture in FR4. Many in the industry feel that moisture within the PCB is not much of an issue, and thus leading me to believe that the CTE should change very little. Steve A

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Earl Moon

#15259

Re: TCE for Ais | 25 June, 1998

| | Hi there, | | Does any one know what is TCE for fully wet saturated FR4. I came to know that for Dry FR4 the TCE is about 15-19 PPM �C. Is that true? | | | | Appreciated for your help. | | rgs, | | chiakl | Chiakl, | It looks like you are speaking of what could also be | termed as "Coefficient of Thermal Expansion (CTE). | This is commonly expressed in cm /(cm * C) or dimensional | change per degree of temperature change. One of my sources | of information states that FR4 is in fact 16. My guess is | that FR4 was engineered to match the CTE of copper. | I am not aware of any studies of CTE reguarding moisture in | FR4. Many in the industry feel that moisture within the PCB | is not much of an issue, and thus leading me to believe that | the CTE should change very little. | Steve A Back in the good old days, when I was a lad, TCE was the term denoting thermal coefficient of expansion just as TCR for resistance and what happened to foot/lbs of torque no reversed. Anyway, Steve is right. Copper foil has a TCE/CTE of 17-19 ppm/C. while typical resin systems (most all including FR-4, polyimide, BT, modified epoxies, etc.) expand at 15-17 in the x and y axes. Moisture is not an issue concerning TCE/CTE as most resin systems (those mentioned above) are between .2-.5% hygroscopic. The most deleterious effect of this moisture is outgassing in poorly drilled, prepared, and plated hole walls. It also is critical in flexible and rigid/flex circuitry but does not concern TCE. Please do not confuse moisture with improperly cured laminate or MLB's. If boards do not reach full cure (molecularly x-linking) all axes suffer and movement is excessive though other problems will be obvious as delamination, pad lifting, etc.. Earl Moon

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