Technical Library | 2019-05-01 23:18:27.0
Moisture can accelerate various failure mechanisms in printed circuit board assemblies. Moisture can be initially present in the epoxy glass prepreg, absorbed during the wet processes in printed circuit board manufacturing, or diffuse into the printed circuit board during storage. Moisture can reside in the resin, resin/glass interfaces, and micro-cracks or voids due to defects. Higher reflow temperatures associated with lead-free processing increase the vapor pressure, which can lead to higher amounts of moisture uptake compared to eutectic tin-lead reflow processes. In addition to cohesive or adhesive failures within the printed circuit board that lead to cracking and delamination, moisture can also lead to the creation of low impedance paths due to metal migration, interfacial degradation resulting in conductive filament formation, and changes in dimensional stability. Studies have shown that moisture can also reduce the glass-transition temperature and increase the dielectric constant, leading to a reduction in circuit switching speeds and an increase in propagation delay times. This paper provides an overview of printed circuit board fabrication, followed by a brief discussion of moisture diffusion processes, governing models, and dependent variables. We then present guidelines for printed circuit board handling and storage during various stages of production and fabrication so as to mitigate moisture-induced failures.
Technical Library | 2015-02-27 17:06:01.0
The drive towards fine pitch technology also affects the soldering processes. Selective soldering is a reliable soldering process for THT (through hole) connectors and offers a wide process window for designers. THT connectors can be soldered on the top and bottom side of boards, board in board, PCBs to metal shields or housing out of plastic or aluminum are today's state of the art. The materials that are used to make the solder connections require higher temperatures. Due to the introduction of lead-free alloys, the boards need more heat to get the barrels filled with solder. This not only affects the properties of the flux and components, but the operation temperatures of solder machines become higher (...)First the impact of temperature will be discussed for the separate process steps and for machine tooling. In the experimental part measurements are done to verify the accuracy that can be achieved using today's selective soldering machines. Dedicated tooling is designed to achieve special requirements with respect to component position accuracy.
Technical Library | 2014-02-06 17:49:48.0
Many electronics manufacturers perform SIR testing to evaluate solder materials and sometimes the results they obtain differ significantly from those stated by the solder material provider. The difference in the results is typically the result of SIR coupon preparation. This paper will discuss the issue of SIR coupon preparation, board cleaning techniques, and how board cleanliness directly affects SIR results.
Technical Library | 2008-05-07 17:54:58.0
Tracking goods through manufacturing was originally accomplished with pencil, paper and human input. Barcodes introduced an automated, machine-readable tracking mechanism that streamlined all types of manufacturing. But modern printed circuit board (PCB) assemblies are running into limitations because of barcode labels. And though barcodes and RFID tags will co-exist, the relatively large barcode labels have to find increasingly scarce real estate on high density boards.
Technical Library | 2010-04-15 20:42:44.0
The high level of current interest in embedded passives in printed circuit boards is driven by the tremendous pressure to pack more circuitry into smaller spaces. However, adoption has been limited due to design, prototyping and infrastructure issues, as well as the stability and tolerances necessary for widespread replacement of discretes. The focus of this work has been to develop a polymer thick film resistor technology to incorporate reliable organic resistors inside printed wiring boards using standard PWB processing.
Technical Library | 2013-10-13 10:36:21.0
Designing circuit boards for selective robotic spraying of conformal coating can be straightforward if you follow some design rules. Follow them and you can save money and time in your application process. However, if the rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Technical Library | 2024-01-08 21:31:01.0
The aim of this collection and interpretation is to develop an understanding of moisture in materials, especially in printed circuit boards, to know the effects on further processing and to be able to derive targeted corrective actions when moisture-related problems occur. In principle, the considerations are valid for all types of PCBs. Although these basic principles are of particular importance when working with flexible and rigid-flexible printed circuit boards; observing them can mean the difference between success or failure.
Technical Library | 1999-05-07 08:45:39.0
Fine pitch SMT devices, although certainly not new, present more of an assembly processing challenge than 50 mil pitch devices. In fact it seems that the finer the pitch the more difficult or narrower the process window becomes. Besides the pitch of the leads being less on fine pitch devices narrower pad width on the board is typical. With fine pitch designs the board fabrication process is also stressed in that the strip of mask between the pads is designed narrower, the alignment of the mask to copper becomes more critical
Technical Library | 1999-05-07 11:24:21.0
Many manufacturers have now completed the conversion to no clean solder paste. Many factors governed this initial conversion, among those being cosmetics, solder ability, and process ability. In circuit testing or probing through no clean solder paste residues has topically not been a major factor in the conversion decision for several reasons. Due to board design, solder paste was only used on one side of the board and not subjected to testing...
Technical Library | 1999-07-21 09:04:04.0
A high volume manufacturer of printed circuit boards (PCBs) had attempted for many years to locate an adhesive that was robust enough to meet their manufacturing needs. This proved to be a challenge because they needed the adhesive to accommodate a wide range of different dispensing equipment and board designs. The two key performance criteria required from the adhesive were dispensability and adhesion...
.jpg)
