China
Africa
Explore chapters and articles related to this topic
Printed Wiring Board Design and Fabrication
Published in Michael Pecht, Handbook of Electronic Package Design, 2018
Denise Burkus Harris, Pradeep Lall
One sealing material used to solder mask is a dielectric epoxy that is applied to one or both surfaces of the board by film lamination or screen printing. The film lamination is similar to the photoresist process. The polymer is applied in the form of a thin lamination on the surface and imaged using a phototool or mask. The resist is then stripped, exposing only the junctions to be accessed for soldering. The accuracy achieved by this process is excellent, usually less than ±0.001 in. Nevertheless, it is more expensive than the screen printing process.
Coating, Encapsulating, and Marking
Published in Fred W. Kear, Hybrid Assemblies and Multichip Modules, 2020
If a dry film solder mask is used, it is important to ensure that its total thickness does not exceed .003 inch. If the thickness exceeds this limit, there is a strong possibility that it may impede the screening of solder paste and thus affect the soldering of surface-mount components. The seriousness of this problem is dependent on specific attributes of the solder paste screening process and the composition of the solder paste.
The Printed Wiring Board (PWB) in Electronics Manufacturing
Published in Jack Arabian, Computer Integrated Electronics Manufacturing and Testing, 2020
If the process control parameters of the above steps are rigidly controlled and the bare boards pass inspection, they must now be prepared to receive their mounted components such as resistors, capacitors, transistors, and ICs. It is to be remembered that this description is for the mounting of “intrusive pin” components whose leads will be inserted into the through holes previously drilled. In order to be able to connect these components electrically, the board goes through a wave solder operation (see the chapter entitled “Solder and Automated Soldering Processes” under the section entitled “Wave Soldering”). Unfortunately, the wave of molten solder applied to the etched, high-density circuitry and component pins can create “solder bridges,” or short circuits. In order to prevent or reduce the risk of solder bridging, a “solder mask” is used. It serves as a barrier to solder, and it is made of an epoxy system. It is applied to all of the circuitry which does not require wave solder. Only those connection points, such as the drilled, plated holes and surrounding “lands,” remain exposed in order to receive a limited wetting of solder. Solder masking can be applied as a liquid film or as a dry film with adhesive properties. The solder masking step before wave soldering is also a good time to add component location nomenclature or other written legends by silk-screening a legibly colored epoxy on the solder mask surface. If the solder mask is transparent, nomenclature marking can be done on the bare board surface before the solder mask operation (see Chart 1-02 at the end of this chapter). Solder masking is also used for “tenting” or covering of vias (if they are exposed to the outer layer) to prevent deposition of unwanted particles or other contamination in the holes. In addition, tenting applied to unused through holes aids in the vacuum hold-down process during testing of the bare board or assembled PWB (see the chapter entitled “Manufacturing Test” under the section entitled “Bare Board Test IBBT]”).
Automated Dielectric Thermoscopy Characterization of Water-Contaminated Grease
Published in Tribology Transactions, 2019
Nicholas Dittes, Mikael Sjödahl, Anders Pettersson, Defeng Lang
The areas Ag and Ac can be calculated as where the areas of a thin film coating (solder mask) and grease on the surface are assumed to fit within a semicircular profile. The coating thickness is The variables k1 and k2 can be calculated as where w is the width of the digits, and s again is the distance between the traces (edge to edge). The function K in Eq. [1] represents the “complete elliptic integral of the first kind” and is calculated with the estimate in the following equation, using the arithmetic–geometric mean calculated to the fourth order, where k1 and k2 are substituted into the equation and used respectively:
EUROCORR 2018: applied science with constant awareness: part 4*
Published in Corrosion Engineering, Science and Technology, 2019
‘Influence of voltage, electrical field and material aging on humidity-induced failure mechanisms of electronic printed circuit boards (PCBs) during high voltage load’ was described by K. Lux (Robert Bosch GmbH, Schwieberdingen, Germany). Comprehensive temperature humidity bias experiments were performed with variations in solder mask application, stress voltage and pre-aging. In masks of identical construction, doubling the voltage load significantly increased the anodic migration. Application of 1000 V to an 800μm-line test structure with thick mask, led to anodic migration between the copper tracks, whereas no between-track migration was observed upon application of 500 V to the thick-masked 400μm-line test structure; this despite the latter giving an identical electrical field. Since the same curing parameters were used for both masks, incomplete cross-linking of the thick mask is suspected to increase water-absorption and anodic migration.
EUROCORR 2017 in combination with the 20th International Corrosion Congress and the Process Safety Congress 2017: Corrosion Control for safer living part 3
Published in Corrosion Engineering, Science and Technology, 2018
‘The influence of solder mask and hygroscopic flux residues on water layer formation on Printed Circuit Board Assembly (PCBA) surface and corrosion reliability of electronics’ was described by Kamila Piotrowska (Technical University of Denmark). Climatic testing was performed in the presence of adipic and glutaric acid under various relative humidity at 25 and 40°C using gravimetric water vapour sorption/desorption and electrochemical impedance methods. The corrosivity of Weak Organic Acids (WOAs) was evaluated via leakage current measurements using surface insulation resistance (SIR) comb patterns. The corrosive properties of solder flux systems were correlated with their hygroscopicity and solubility, both of which relate to the chemical structure of the organic acids. Increased temperature was found to increase the WOAs solubility and cause a stronger interaction with water molecules, shifting the critical RH level for deliquescence and efflorescence towards the lower humidity range. Moreover, an increase of temperature accelerates corrosion, allowing the WOAs to dissolve at lower RH levels.