Technical Library | 2019-07-10 23:36:14.0
Pockets of gas, or voids, trapped in the solder interface between discrete power management devices and circuit assemblies are, unfortunately, excellent insulators, or barriers to thermal conductivity. This resistance to heat flow reduces the electrical efficiency of these devices, reducing battery life and expected functional life time of electronic assemblies. There is also a corresponding increase in current density (as the area for current conduction is reduced) that generates additional heat, further leading to performance degradation.
Technical Library | 2023-01-17 17:12:33.0
Reflowed indium metal has for decades been the standard for solder thermal interface materials (solder TIMs or sTIMs) in most high-performance computing (HPC) TIM1 applications. The IEEE Heterogeneous Integration Thermal roadmap states that new thermal interface materials solutions must provide a path to the successful application of increased total-package die areas up to 100cm2. While GPU architectures are relatively isothermal during usage, CPU hotspots in complex heterogeneously-integrated modules will need to be able to handle heat flux hotspots up to 1000W/cm2 within the next two years. Indium and its alloys are used as reflowed solder thermal interface materials in both CPU and GPU "die to lid/heat spreader" (TIM1) applications. Their high bulk thermal conductivity and proven long-term reliability suit them well for extreme thermomechanical stresses. Voiding is the most important failure mode and has been studied by x-ray. The effects of surface pretreatment, pressure during reflow, solder flux type/fluxless processing, and preform design parameters, such as alloy type, are also examined. The paper includes data on both vacuum and pressure (autoclave) reflow of sTIMs, which is becoming necessary to meet upcoming requirements for ultralow voiding in some instances.
Technical Library | 2023-09-07 14:54:10.0
A global manufacturer of a broad line of electronic interconnect solutions worked with us to dispense conductive adhesive EpoTek H20E-FC. EpoTek H20E-FC is a two-component, electrically conductive, snap curing epoxy for photovoltaic thin film module stringing, semiconductor packaging and PCB circuit assembly. The primary goal was filling a rectangular cavity on a connector. The epoxy needed to fill the connector to the top of the walls in less than three seconds.
Technical Library | 1999-08-27 09:24:56.0
Dispensing conductive adhesives in an automated factory environment creates some special challenges. A robust production process starts with understanding the adhesives in their fluid state and which important parameters must be controlled. Developing this understanding requires experience with a large number of materials and valves over time. Common uses of conductive adhesives in surface mount applications, die attach applications, and gasketing are addressed. As vendors of dispensing equipment, the authors see a constant stream of such applications. Dispensing requirements, techniques, and equipment resulting from this experience are discussed. Guidelines for optimizing quality and speed are given.
Technical Library | 2019-06-04 10:19:46.0
Interconnection technology relies very heavily on the ability of the conductors on a printed wiring assembly to maintain reliable signal integrity. Harsh environmental factors can precipitate a loss of conductivity due to oxidation and corrosion. Connections are typically soldered or inserted using pressure fitted connectors to obtain enough surface contact to meet the electrical conductivity requirements. In pressure contacts, surface integrity is especially critical where the abrasive effects of retraction and insertion can wear off the metallic finish from the contact area. This can expose the underlying copper or nickel and lead to increased resistance at the contact points. These types of conductors are frequently found in card edge connectors where the terminations are plated with a layer of nickel and gold (frequently referred to as gold fingers). A hard gold is typically used containing very small amounts of nickel and cobalt to increase the wear resistance.
Technical Library | 2019-06-19 11:06:46.0
Tin (Sn) metal displays the characteristic of growing “tin whiskers” from pure tin coatings (most actively on relatively thin, electrodeposited or immersion tin coatings), usually months or years from the initial deposition of the tin. Tin whiskers are electrically conductive, filamentary, single crystals of white (beta phase) tin. These filaments of single crystal tin are usually one to five microns in diameter, and a few microns up to several tens of millimeters long, that grow spontaneously from the tin coatings. Alloying additions of several percent (by weight) of lead (Pb) prevents these electrically conductive tin whiskers from growing. Pb alloyed into the Sn was discovered to prevent the occurrence of tin whiskers in electronic assemblies in the 1950s as the Bell Laboratories solution to the problem of tin whiskers. The alloying of the tin with lead has thus quietly averted incalculable losses from short circuits in electronic equipment for the last 60 years.
Technical Library | 2019-06-03 15:32:40.0
ACI Technologies was pleased to assist a customer by conducting elemental analysis on several assemblies displaying severe corrosion. Several board assemblies had failed in the field and exhibited areas of corrosion in close proximity to onboard components. The most common source of corrosion on electronic assemblies is residual flux. Fluxes are specific chemistries applied during the soldering process which improve the wetting of the solder to both the pad and component when forming the solder joint. They can be highly reactive chemicals that, if left on the assemblies, can lead to corrosion, electrical degradation, and decreased reliability. In the presence of moisture and electrical bias, flux residue can enable dendritic growth as a result of electrochemical migration (ECM).
Technical Library | 2019-05-21 17:38:55.0
Last month we presented Flip Chip Rework.As promised, this month we follow up with attachment techniques. Flip chip assembly is a key technology for advanced packaging of microelectronic circuits. It allows attachment of a bare chip to a packaging substrate in a face-down configuration, with electrical connections between the chip and substrate via conducting “bumps.” Flip chip technology was first invented by IBM for mainframe computer application in the early 1960s. Semiconductor devices are mounted face down and electrically and mechanically connected to a substrate (Figure 1). IBM called this manufacturing process a C4 process (controlled collapse chip connection).
Technical Library | 2019-06-12 10:33:58.0
The success of ball grid array (BGA) placement on electronic assemblies is as much a matter of proper preparation and planning, as it is technique. In some designs, it is more appropriate to apply BGAs using a rework station that isolates the placement of the device, without subjecting the entire assembly to thermal reflow. This is especially beneficial in board constructions where the number of BGAs is limited, and the application of the solder paste is difficult, due to small pitch features that stretch the limitation of the stencil construction. Another application for rework stations, involves very large and thermally conductive BGAs, which will not uniformly reflow with other components on the assembly, and may require special process parameters for their proper placement. The most common use of BGA rework stations are for assemblies requiring BGA removal and replacements due to failures in the initial assembly stage.
Technical Library | 2019-09-16 09:41:02.0
“What is Virtual Manufacturing?” The simplest answer is a manufacturing simulation using a computer. The more complete answer is that virtual manufacturing is the process of designing a model of a real system and conducting experiments with this model for the purpose of understanding the behavior of the system. In today’s complex manufacturing environment, processes must be completely understood before implementation in order to “get it right the first time.” To achieve this goal, the use of a virtual environment is essential for simulating individual manufacturing processes and the total manufacturing system. By driving compatibility between the product design and the assembly plant process, these virtual tools enable the early optimization of cost, quality, and time to help achieve integrated products, process and resource design, and affordability.
