Surface-mount adhesives specifications

The first specifications for adhesives were generated by the staff of NASA and the DoD who were prompted by the high reliability that was required of microcircuits used in aerospace programs. These specifications covered primarily die and substrate attachments for hermetically sealed integrated circuits, hybrid microcircuits, and multichip modules. Subsequently, with the increased use of surface-mount adhesives in the assembly of commercial printed-wiring boards and underfills for flip-chip devices, industry associations took the lead in generating the requirements and test methods. 

For example, solvent or chemical resistance of adhesives used in surface-mount assembly may be tested according to Method 4.5.6 of ANSI/ lPC-SM-817, General Requirements for Dielectric Surface-Mounting Adhesives Although this method specihes specific solvents including isopropanol 1,1,1-trichlorotrifluoroethane an azeotrope of 6% methyl alcohol and 94% trichlorotrifluoroethane and a 10% alkaline... 

Specifications for surface-mount adhesives. With the advent and wide use of surface-mount adhesives, several industry and industry-association documents have been generated. Examples include the following ... 

IPC-3406 Guidelines for Electrically Conductive Surface Mount Adhesive IPC-3407 General Requirements for Isotropically Conductive Adhesives lPC-3408 General Requirements for Anisotropically Conductive Adhesive Films lPC-4101 Specification for Base Materials for Rigid and Multilayer Boards lPC-4103 Specification for Plastic Substrates, Clad or Unclad, for High Speed/High Frequency Interconnection... 

Thus, components that are surface mounted with adhesives must maintain their strength and electrical properties during and after these combined environments and after repeated stresses. To assure reliabiUty, numerous accelerated tests have been developed and incorporated in military and industry specifications. Among specifications governing the mechanical, electrical, and quaUfication requirements for electronic components, modules, subsystems, and systems, most of which could not be met without using qualified and reliable adhesives, are MIL-STD-883, MIL-STD-810, MlL-STD-202, and MIL-PRF-38534. ... 

Numerous geometrical factors of the specific interconnection will also influence anisotropic adhesive formulation and processing, including lead planarity, IC pad metallization, and IC test patterns. The planarity of the leads on the substrate and/or device and the compliance of the conductive particles will determine if anisotropically conductive adhesives can be used in a particular application. For systems with large disparities between lead height, no electrical interconnection will be formed, as shown in Fig. 5. Fine-pitch IC packages for surface-mounted applications, such as the plastic quad flat pack (PQFP), often use gullwing leads that olfer much compliance to the joint. Even if the... 

Efforts to bond rubber to metal without the use of metal plating led to what is believed to be the first research efforts in surface preparation prior to adhesive bonding. Strong and durable bonds of rubber to metal were necessary for rubber shock mounts for automobiles in the late 1920s, but they were limited to proprietary formulations used on specific metals. In 1927 solvent-based thermoplastic rubber cements for metal-to-rubber bonding were prepared from rubber cyclized by treatment with sulfuric or other strong acids. With these rubber cements strong bonds could be made to either vulcanized or unvulcanized rubber. 

---