Technical Library | 2019-08-07 22:56:45.0
The requirement to reconsider traditional soldering methods is becoming more relevant as the demand for bottom terminated components (QFN/BTC) increases. Thermal pads under said components are designed to enhance the thermal and electrical performance of the component and ultimately allow the component to run more efficiently. Additionally, low voiding is important in decreasing the current path of the circuit to maximize high speed and RF performances. The demand to develop smaller, more reliable, packages has seen voiding requirements decrease below 15 percent and in some instances, below 10 percent.Earlier work has demonstrated the use of micro-fluxed solder preforms as a mechanism to reduce voiding. The current work builds upon these results to focus on developing an engineered approach to void reduction in leadless components (QFN) through increasing understanding of how processing parameters and a use of custom designed micro-fluxed preforms interact. Leveraging the use of a micro-fluxed solder preform in conjunction with low voiding solder paste, stencil design, and application knowhow are critical factors in determining voiding in QFN packages. The study presented seeks to understand the vectors that can contribute to voiding such as PCB pad finish, reflow profile, reflow atmosphere, via configuration, and ultimately solder design.A collaboration between three companies consisting of solder materials supplier, a power semiconductor supplier, and an electronic assembly manufacturer worked together for an in-depth study into the effectiveness of solder preforms at reducing voiding under some of the most prevalent bottom terminated components packages. The effects of factors such as thermal pad size, finish on PCB, preform types, stencil design, reflow profile and atmosphere, have been evaluated using lead-free SAC305 low voiding solder paste and micro-fluxed preforms. Design and manufacturing rules developed from this work will be discussed.
Technical Library | 2007-11-15 15:54:44.0
At the contractor level once a product is required to be soldered with lead-free solders all the processes must be assessed as to insure the same quality a customer has been accustomed to with a Sn63Pb37 process is achieved. The reflow, wave soldering and hand assembly processes must all be optimized carefully to insure good joint formation as per the appropriate class of electronics with new solder alloys and often new fluxes.
Technical Library | 2009-07-09 17:23:07.0
Sometimes you just cannot clean with water. Good examples of this are: circuits with batteries attached, cleaning prior to encapsulation, ionic cleanliness testing, and non-sealed or other water sensitive parts. High impedance or high voltage circuits need to be cleaned of flux residues and other soils to maximize performance and reliability and, in these types of circuits; water can be just as detrimental as fluxes. When solvent cleaning is called for, Hansen solubility parameters can help target the best solvent or solvent blend to remove the residue of interest, and prevent degradation of the assembly being manufactured. In short, using this approach can time, manufacturing cost and reduce product liability.
Technical Library | 2013-04-11 15:43:17.0
With the explosion of growth in handheld electronics devices, manufacturers have been forced to look for ways to reinforce their assemblies against the inevitable bumps and drops that their products experience in the field. One method of reinforcement has been the utilization of underfills to "glue" certain SMDs to the PCB. Bumped SMDs attached to the PCB with a no-clean soldering process offer the unavoidable scenario of the underfill coming in contact with a flux residue. This may or may not create a reliability issue... First published in the 2012 IPC APEX EXPO technical conference proceedings
Technical Library | 2021-11-03 16:49:59.0
Ultrathin bare die chips were soldered using a novel soldering technology. Using homogeneous flash light generated by high-power xenon flash lamp the dummy components and the bare die NFC chips were successfully soldered to copper tracks on polyimide (PI) and polyethylene terephthalate (PET) flex foils by using industry standard Sn-Ag-Cu lead free alloys. Due to the selectivity of light absorption, a limited temperature increase was observed in the PET substrates while the chip and copper tracks were rapidly heated to a temperatures above the solder melting temperature. This allowed to successfully soldered components onto the delicate polyethylene foil substrates using lead-free alloys with liquidus temperatures above 200 °C. It was shown that by preheating components above the decomposition temperature of solder paste flux with a set of short low intensity pulses the processing window could be significantly extended compared to the process with direct illumination of chips with high intensity flash pulse. Furthermore, it was demonstrated that with localized tuning of pulse intensity components having different heat capacity could be simultaneously soldered using a single flash pulse.
Technical Library | 2021-07-27 14:54:26.0
Fast forward to current time. Today, our society embraces cleanliness. We expect, demand, and evaluate cleanliness in almost every aspect of our lives. We wash our cars and pets. We maintain high cleanliness standards in our hotels and public spaces. We require cleanliness in our restaurants and hospitals. We sanitize our hands throughout the day to prevent illness. We live in a clean-centric culture. While we drive clean cars, stay in clean hotels and eat clean food, there is one part of our life where we actually abandoned cleanliness. Many of the circuit assemblies that affect almost every aspect of our daily lives are no longer required to be clean. Even though our life experience confirms the link between cleanliness and reliability, happiness, health, and safety, circuit assemblies no longer maintain that "cleanliness is next to Godliness" status. This was not always the case. There was a time when virtually all circuit assemblies were cleaned. The removal of flux and other process-related contamination was commonplace. Cleaning was as normal as soldering. As we bring history into current time, one may relate the fall of Rome and its adoption of personal hygiene and the subsequent decline in human health to the large-scale abandonment of cleanliness expectations of circuit assemblies and the subsequent reliability issues it has created. How did this happen? Has history repeated itself?
Technical Library | 2007-08-09 12:23:10.0
Recent developments in No Flow-Fluxing Underfill (NFFUF) products have demonstrated their utility to enhance the reliability of flip chip assemblies with reduced processing steps over conventional capillary flow methods. This basic work considered processing conditions such as dispensed volume and placement force, speed and dwell time. Further evaluations of these new products on a variety of flip chip assembly configurations manufactured by various processes have been undertaken to provide further evidence of their suitability and potential in high volume electronic manufacturing. This paper summarizes the recent evaluations and discusses new studies of additional assembly configurations, which include higher input/output (l/O) counts up to full arrays in excess of 1200 l/Os.
Technical Library | 2007-10-18 13:42:45.0
To successfully achieve lead-free electronics assembly, each participant in the manufacturing process, from purchasing to engineering to maintenance to Quality/Inspection, must have a solid understanding of the changes required of them. This pertains to considerations regarding design, components, PWBs, solder alloys, fluxe s, printing, reflow, wave soldering, rework, cleaning, equipment wear & tear and inspection.
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 | 2017-01-05 16:55:11.0
The July 2006 implementation of ROHS exempted automotive applications from converting to lead free technology. Nine years later, all major OEM and Tier 1 automotive manufacturers have converted or are in the process of converting to lead free circuit assembly processing. Starting with SAC (SnAgCu) alloys as a baseline for lead free soldering, in the last years several specific alloys were developed in order to improve resistance to high temperature creep, vibration survival and the ability to withstand thermal cycling and thermal shock.The paper compares three different solder alloys and two flux chemistries in terms of void formation and mechanical / thermal fatigue properties. Void content and reliability data of the alloys will be presented and discussed in relation to the acceptance criteria of a Tier 1 /OEM automotive supplier. As a result, a ranking list will be presented considering the combined performance of the alloys. In order to analyze the void formation and mechanical behavior of different solder alloys and flux chemistry combinations, statistical methods are used.
