22 декабря, 2015 
Pokraskin The electrical characteristics of electronic components with solder bumps such as flip chips or ball grid arrays (BGAs) must remain stable in the long term. However, heat cycles, vibrations or direct mechanical stress used to have a negative effect on the durability. When these components are soldered onto a circuit plate, any gaps will remain between the bumps. So as to ensure as stable an interconnection between the components as possible, so-called ‘underfill materials’, which are based on epoxy adhesive technology, are used to completely fill the space between the bumps and to protect the solder joint. Two methods are available:
• No-flow process: Application of the underfill adhesive before the soldering process. When the components are applied, the adhesive is pressed into the gaps using a paste-like material (e. g. a one-part epoxy adhesive), followed by a thermal curing of the adhesive.
• Capillary process: The material (e. g. two-part epoxy adhesive) is injected into the gaps between the bumps by means of a metering needle following the soldering process, and then cured.
The adhesives are required to build up good adhesion to the substrates, and to be shock and vibration resistant, respectively.
8.7.4
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