Dougal Stewart,
  
>    On another issue, I always get confused when people talk about FR3, 
>    G10, G200, CEM 1, CEM3 etc. I know what FR4 is - glass fibre
>    reinforced epoxy laminate - but could someone put the other 
>    materials into similar English for me?
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  
  Robert,
  
    Hopefully I can give a bit of information to you that may help, I was 
  in the same boat too...I had to dig around in some old NEPCON proceedings 
  to freshen-up a bit, so here goes:
  
  
    First off, FR-4 is a widely used generic term to describe the standard 
  epoxy/fiberglass/copper laminate...but it doesn't fully or accurately 
  describe the material. 
  
    "FR" really stands for "Fire-retardant", and the "4" designates an 
  electronic grade glass fiber that has been woven into cloth. Prior to 
  that, back in the early days, UL began to require laminate materials to 
  be fire retardant in which chemicals such as bromine were added to a 
  kraft or alpha-cellulose paperbase material impregnated with a phenolic 
  resin and designated FR-2. Epoxy was then used with the paperbased 
  material and designated FR-3.
  
    There are several grades of fiberglass reinforced laminates in which 
  the designations change depending on the bonding resins used. 
  
  Here are several:
  
  * G-5 - Uses a melamine resin and has great mechanical properties, but is 
          difficult to machine or drill. The military calls it GMG and GME  
          styles.
  
  * G-7 - Uses a silicone resin.
  
  * G-10 - Uses an epoxy resin as FR-4 does, but it is not fire retardant.
  
  * G-11 - Also uses and epoxy resin but has better mechanical properties   
           than does G-10, it is also harder to machine.
  
  * FR-5 - Is the Fire retardant version of G-11.
  
  * GPO-1 - Uses a polyester resin and a fiberglass "mat" material and is   
            less expensive than woven cloth. The mat material is chopped    
            into bits and randomly layered.
  
  * Expanded Teflon - With a Polytetrafluoroethylene resin (PTFE resin) is   
                      one of the highest costing materials and has excellent 
                      low dielectric constant properties for high frequency  
                      microwave circuits, but suffers from poor dimensional  
                      stability...it can shrink 1-2% after copper etching.
   
  
  A bit about the reinforcing materials.....
  
    Fiberglass accounts for around 95% of the reinforcing material used in 
  PC board laminates. The fiberglass is designated into two types; E-glass 
  and S-glass, both are made of soda lime fibers bundled into yarn and 
  woven into cloth. 
  
    The E designates it as electrical class, and the S designates it as 
  high strength class. There is another type glass that is designated D 
  class which offers a lower dielectric constant, but it is not as strong 
  as either the E or S class glass....(say that 10-times real fast!!) 
  
    Of course there are different grades of weave density which determines 
  how smooth the surface of the laminate is, how many layers are 
  laminatable, and the CTE in the Z-axis. 
  
    Other reinforcing materials used in special applications include: 
  quartz, aramid (kevlar 29 & 49) fiber, ceramic, insulated steel, anodized 
  aluminum, and copper bonded to flexible substrates such as mylar or 
  polyimide.
  
  
  A bit about the bonding resins.....
  
    Difunctional epoxy has been the most widely used type of epoxy for 
  board laminates. The type of epoxy chosen is based on the requirements 
  needed for the assembly. Two other types of epoxy's are used which are 
  known as multifunctional, and tetrafunctional epoxy, each type having a 
  progressively higher Tg than the previous one. 
  
  There are five areas that are analyzed when deciding the type of resin to 
  be used in the laminate: 
  
  
 Glass transition temperature 
  
 Relative dielectric constant
  
 Loss tangent
  
 Thermal conductivity 
  
 coefficient of thermal expansion
  
  A few other types of resin used in special applications are:
  
  * Bismaleimide Triazine (BT) resin also known as cyanate ester resin.
  
  * Polyimide resin (also used in Kapton tape and TAB)
  
  * Polysulfone (a thermoplastic polymer resin)
  
  * Polyetherimide (also a thermoplastic polymer resin)
  
  
  Well, I'm about tapped-out as far as anymore knowledge on laminates... 
  Most of the time, the only thing I'm concerned with about PC boards is 
  whether or not the darn things solder good!!
  
                                     I hope this was of some help,
  
  
  
                               ////  
 
                              |  @@ /      Steve Gregory  
                              C   )        Process Training Engineer
                 ////  
       \_o         Pragmatech Incorporated
                |  @@ /                    101 Nicholson Lane
                C   )                      San Jose, California 95134
                 \_o        ////  
        [log in to unmask]  
                           |  @@ /         Phone:(408) 943-1151             
                           C   )           Fax:(408)943-1461   
                            \_o