Alex - My two cents:

The bottom line is the power dissipation of the chip resistor in the circuit. Assuming for argument's sake, that the resistor is an 0805 with a rating of 1/10 watt, and the resistor is dissipating near the full wattage, the resistor element (on glass laminate) needs to be face up. Glass laminate, like FR4, is a good thermal insulator. If the power dissipation is, for argument's sake, less than 1/2 the rated wattage, then it shouldn't make any difference, and the resistor should be a process indicator. If the resistor is mounted on a ceramic (Alumina) substrate, then the resistor can be mounted either way with virtually no effect, except aesthetics. Ceramic (Alumina), unlike FR4, is a good thermal conductor.

Ed Valentine
Electronics Manufacturing Solutions
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  ----- Original Message ----- 
  From: Alex Krstic 
  To: [log in to unmask] 
  Sent: Thursday, January 25, 2001 4:12 PM
  Subject: [TN] Placement of Chip resistors deposited element


  Hello all.  We recently received some boards with some of the chip resistors placed with their resistive elements towards the board.  J-STD-001B and C view this as violation for both Class 2 and Class 3.  However when you compare this with IPC-A-610C it is only a process indicator for Classes 2 and 3.  The relevant sections are 

   

  J-STD-001C 

   

  6.4.2.2 Devices with External Deposited Elements

   

  IPC-A-610C

   

  12.3.2 Chip Components - Termination Variations - Deposited Electrical Elements - Mounting Upside Down.

   

  So...who is correct?  Does it matter?

   

  Alex Krstic

   

  NovAtel Inc.