Assembly process Thermal tests

Historically, the properties that received the greatest amount of attention were the glass transition temperature, Tg, and the coefficients of thermal expansion, or CTEs, particularly in the z-axis. With the advent of lead-free assembly processes, other properties have increased in importance as well.The most notable is the decomposition temperature,Ta.These properties were described in more detail in Chap. 6, and will be discussed again in Chap. 10, which focuses on the impact of lead-free assembly on base materials. However, some additional information as well as examples of the test data are included here, as well as comparisons of some common material types. 

The solder shock test is one of several methods to assess the thermal resistance of copper-clad laminates. It is easy to perform and represents another key test during the early assessment of a material. There are a number of different methods to choose from, which will be described in detail in Section 12.5.2. During the initial assessment of the material, it is important to choose at least one of the described test methods to make certain that the material meets the minimum requirements, especially if the material is nsed in higher-temperatnre lead-free assembly processes. Aside from solder shock testing of bare laminate material, it is also recommended that the PCB engineer consider PCB-level temperatnre shock as well as repeated reflow testing with a particnlar focns on resin-reinforcement delaminations. This will ensnre that not only the raw material bnt also the completed PCB will be able to withstand the required temperatnre regime. 

Solder Float Resistance. This test addresses the thermal resistance of the laminate material floating on the solder bath. Becanse this method subjects the sample to a thermal gradient across the z-axis of the material similar to an actual wave solder operation, the resnlts of this test are particnlarly important and—as mentioned previously—either solder pot temperatures or exposure times should be increased if the laminates are intended for use in lead-free assembly processes. 

Laboratory and field testing determined the effectiveness of a new decontamination process for soils containing 2,4-D/2,4,5-T and traces of dioxin. The process employs three primary operations - thermal desorption to volatilize the contaminants, condensation and absorption of the contaminants in a solvent, and photochemical decomposition of the contaminants. Bench-scale experiments established the relationship between desorption conditions (time and temperature) and treatment efficiency. Laboratory tests using a batch photochemical reactor defined the kinetics of 2,3,7,8-TCDD disappearance. A pilot-scale system was assembled to process up to 100 pounds per hour of soil. Tests were conducted at two sites to evaluate treatment performance and develop scale-up information. Soil was successfully decontaminated to less than 1 ng/g... 

Fully equipped facility with the capabilities to perform complex material and process testing and evaluations as well as simulating complete flowsheets that can be assembled to represent a commercial plant with many different unit operations. The test center is designed to perform comminution, agglomeration, and thermal processing studies.)... 

The use of underfill adhesives has resulted in the development of the draft version of J-STD-030, Guideline for Selection and Application of Underfill Material for Flip Chip and Other Micropackages. The guideline covers critical material properties for underfill materials to assure compatibility in underfill applications for reliable electronic assemblies as well as selected process-related qualification tests such as thermal cycling. Table 6.9 summarizes selected materials requirements for underfill adhesives from the proposed JEDEC J-STD-030. ... 

The reliability of electronic systems depends on extensive testing, inspection, and evaluation of all parts of the design and manufacturing process, including the adhesives used in the systems. Test methods for adhesives and adhesive-bonded assemblies may be generally classified as physical, electrical, environmental, thermal, mechanical or thermomechanical, and chemical (Table 7.1). This chapter summarizes most of the methods used to test and evaluate adhesives used in electronics. It is not intended to provide detailed instructions, but to lead the reader to the appropriate government or industry specifications, documents that are available from the various organizations listed in Table 7.2. 

Solid polymerie materials undergo physieal and chemical changes when heat is applied. This usually results in undesirable changes to the material s properties. The American Society for Testing and Materials describes thermal degradation as a process whereby the action of heat or elevated temperature on a material, product or assembly causes a loss of physical, mechanical or electrical properties and describes thermal decomposition as a process of extensive chemical species change caused by heat. ... 

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