Polyimides glass laminate properties

Board material The FR-4 versus polyimide board material properties did not have a significant impact on trace temperature, which is determined primarily by the thermal conductivity of the dielectric laminate material construction. Table 16.2 lists measured thermal conductivity values for each of the test boards.The column labeled kz presents values through the thickness of the board and represents the resin thermal conductivity.The values in columns kx and ky are in-plane and the difference is attributed to the influence of the glass fiber. 

Methods of preparation of the laminates depend on the partieular grade of polyimide resin used but in one process the polyimide precursor is dissolved in acetone and this solution is used to impregnate the glass or carbon fibre and thus produce a pre-preg . The pre-preg is dried and then pre-cured at about 200°C for about 3 hours. This operation reduces the volatile content and also modifies the flow properties to make them more suitable for the subsequent... 

Kevlar, or aramid as it is generically known, is a highly oriented polymer - poly(p-phenylene terephthalamide). Kevlar fiber has the interesting property of having a linear TCE in its axial direction of -2 x 10 6/°C. The E-glass used in normal PWBs has a positive linear TCE of +5 x 10-room temperature TCEs in the X-Y plane of around 4 to 8 x 10 6/ C(3) and solder joint cracking is greatly reduced or eliminated(2). Quartz is another reinforcement, available in fabric form, which can be used to control the planar TCEs of a laminate PWB. Quartz has a TCE of +0.54 x 10-6/°C in the axial direction. 

Laminates contain different reinforcement materials (woven/non-woven glass/organic fibers, expanded PTFE, etc.), resin types (phenolic, epoxy, cyanate ester, polyimide, BT, etc.), resin formulations (blended, functionality, etc.), hardeners (dicyanodiamide [dicy],phenol-novolak, cresol-novolak, p-aminophenol, isocyanurate, etc.), and sometimes fUler particles (ceramic or organic). The ratio of aU of these individual components can vary widely.To define a test strategy for laminates, it is important to understand the different main components of the materials as well as the conditions during manufacturing, as these wiU have a large influence on their properties and quality. 

The second method is based on the use of polyimides with lower glass transition temperatures that can be melt-processed. For example, intrinsically photosensitive preimidized polymers formed by reacting 3,3 4,4 -benzopheno-netetracarboxylic acid dianhydride (BTDA) with methyl-substituted 4,4 -methylenebisbenzeneamine (MDA), blended to epoxy resins, give high strength laminate with copper. Poly(isoimides), which exhibit good melt-flow properties before thermal isomerization to imides, are also used to make flexible circuits. In the last process copper is electroless plated on polyimide film such as Kapton 200H. 

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