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???
07/09/04 17:41
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#73895 - RE: Heat damaging components
Responding to: ???'s previous message
Hallo Slobodan,

yes, it's difficult to destroy a 74HC00 in SMD package by standardly soldering with a solder iron.

I don't worry about these parts, but I worry about discretes like big ceramic capacitors! Why? Ceramics and metal end caps are made of material with different thermal properties like heat conduction, heat capacity and thermal elongation. And it's not the absolute temperature what destroys the part, but the fast change of temperature applied to a local point! Enormeous forces develop, if things with different thermal properties joined together are fast and inhomogeneously heated up. Think about the forces freezing water develop...

For achieving high reliability, it's important to introduce some pre-heating before soldering:
Reflow soldering accomplishes a pre-heating phase of 45 seconds to make the temperature of the parts rise from room temperature to 120°C. Wave soldering accomplishes the same pre-heating but over a period of 30sec. From 120°C to 250°C temperature shall rise with a rate of 200K per second.
Vapour phase soldering accomplishes a pre-heating phase of 10 seconds for a temperature change from room temperature to 215°C.

About 1990, when I wasn't well informed about iron soldering of SMD devices, I damaged some 47nF capacitors in 1206 SMD package, because I used standard soldering iron at 350°C.
It's right, that in the moment soldertin is melting, temperature is limited to about 200°C. That's, because energy is converted to make the soldertin melt. But nevertheless, there's this fast temperature shock from room temperarture to about 200°C!
Manufacturers of ceramics capacitors tell, that risk of damage heaviliy increases, if fast temperature fluctuations of >100K are applied. So, it seems to be neccessary, to take care, that solder iron is never touching SMD part directly! Touch the solder pad, instead of SMD part, and apply soldertin...

Todays highest integrated digital chips suffer from another failing mechanism: Moisture having penetrated package, because of wrong storing of chips in unsealed enclosures. If such a chip is soldered, moisture will heat up and steam is produced, which causes overpressure and destroys the ultrasonic bonded wire contacts internally of chip.

Make a google search with "moisture sensitivity level".

Kai

List of 56 messages in thread
TopicAuthorDate
making PCBs for SMD.            01/01/70 00:00      
   RE: making PCBs for SMD.            01/01/70 00:00      
      Adaptors            01/01/70 00:00      
   RE: making PCBs for SMD.            01/01/70 00:00      
      RE: making PCBs for SMD.            01/01/70 00:00      
         RE: making PCBs for SMD.            01/01/70 00:00      
      RE: making PCBs for SMD.            01/01/70 00:00      
   RE: making PCBs for SMD.            01/01/70 00:00      
      RE: making PCBs for SMD.            01/01/70 00:00      
         RE: making PCBs for SMD.            01/01/70 00:00      
   RE: making PCBs for SMD.            01/01/70 00:00      
      RE: making PCBs for SMD.            01/01/70 00:00      
      RE: making PCBs for SMD.            01/01/70 00:00      
         RE: making PCBs for SMD.            01/01/70 00:00      
            RE: making PCBs for SMD.            01/01/70 00:00      
   DS80C400 comes with 100LQFP package!!            01/01/70 00:00      
      I'm not scared :)            01/01/70 00:00      
         RE: I'm not scared :)            01/01/70 00:00      
      RE: DS80C400 comes with 100LQFP package!!            01/01/70 00:00      
         RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
      RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
         RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
            RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
               RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
                  RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
                     RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
                        RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
               RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
                  RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
         RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
      RE: DS80C400 comes with 100LQFP package!!            01/01/70 00:00      
         RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
            RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
         RE: DS80C400 comes with 100LQFP package!!            01/01/70 00:00      
            RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
               RE: DS80C400 comes with 100LQFP package!            01/01/70 00:00      
   Heat damaging components            01/01/70 00:00      
      RE: Heat damaging components            01/01/70 00:00      
      RE: Heat damaging components            01/01/70 00:00      
         RE: Heat damaging components            01/01/70 00:00      
            RE: Heat damaging components            01/01/70 00:00      
               RE: Heat damaging components            01/01/70 00:00      
                  RE: Heat damaging components            01/01/70 00:00      
            RE: Heat damaging components            01/01/70 00:00      
         RE: Heat damaging components            01/01/70 00:00      
            RE: Heat damaging components            01/01/70 00:00      
               RE: Heat damaging components            01/01/70 00:00      
               RE: Heat damaging components            01/01/70 00:00      
                  RE: Heat damaging components            01/01/70 00:00      
            RE: Heat damaging components            01/01/70 00:00      
               RE: Moisture damaging components            01/01/70 00:00      
                  RE: Moisture damaging components            01/01/70 00:00      
                     RE: Moisture damaging components            01/01/70 00:00      
                        RE: Moisture damaging components            01/01/70 00:00      
                           RE: Moisture damaging components            01/01/70 00:00      
                           RE: Moisture damaging components            01/01/70 00:00      

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