Search results

SMT stencil cleaning has traditionally been thought of as a ‘maintenance’ procedure with little or no impact on production. Today, CFC and VOC cleaning processes are being replaced because of environmental concerns, and fine‐pitch and ultra fine‐pitch assemblies are commonplace. These changes in cleaning processes and product specifications have shed new light on the importance of properly cleaning SMT screens and stencils in order to prevent damage to the stencil and potential production‐related problems.This paper takes an unbiased look at the different stencil cleaning processes available through the eyes of an SMT stencil manufacturer. The paper outlines the advantages and disadvantages of using ‘jet spray’ washersvs ‘ultrasonic’ washers, aqueous and semi‐aqueous vssolvent cleaning agents, and the effects of hot wash solutions and hot drying air vsambient wash solutions and drying techniques.Specific criteria evaluated include: cleaning effectiveness of the process; potential adverse effects of the process on the integrity of the stencil; production down‐time and other potential production‐related problems; potential health hazards to users; environmental impact of the process, and waste stream management.Magnified photography is used to demonstrate the relative effectiveness of various cleaning technologies. Third party references of other industry experts, along with the author's own experiences, are cited to support the information provided.

Stencil cleaning has become both more difficult and more critical for modern surface mount technology. There is an increasing need for cleaning agents for stencils which are effective, safe for workers and safe for the environment. This paper describes a new laboratory test which was developed for predicting the performance of stencil cleaning formulations. A new aqueous, inorganic based cleaning agent has been developed which gives cleaning performance which was overall better than that of IPA. Testing was performed over a range of solder pastes. This performance advantage was confirmed with commercial stencil cleaning equipment. In addition to being very effective, this inorganic based stencil cleaner offers significant environmental and worker safety advantages.

Most solder paste printers are configured to periodically clean the stencil to maintain printing quality. However, a periodical cleaning control may result in excessive cleaning operations. The purpose of this paper is to develop a control method to schedule stencil cleaning operations appropriately.

A hybrid failure rate model of the stencil printing process with age reduction factor and failure rate increase factor is presented. A stencil cleaning policy based on system reliability is introduced. An optimization model used to derive the optimal stencil cleaning schedule is provided.

An aperiodic stencil cleaning control with good adaptability is achieved. A comparative analysis indicates that aperiodic control has better printing system reliability than traditional periodical control under the same cleaning resource consumption.

Periodical cleaning control commonly used in industrial printing process often results in excessive cleaning operations. By incorporating the printing system reliability, this paper develops an aperiodic stencil cleaning control method based on hybrid failure rate model of the stencil printing process. It helps to reduce unnecessary cleaning operations while keeping printing quality stable.

Stencil cleaning is an important operation in solder paste printing process. Frequent cleaning may interrupt printing process and increase idle time, as well as loss for performing cleaning. This paper aims to propose a method to optimize the stencil cleaning time and reduce unnecessary cleaning operations and losses.

This paper uses a discrete-time, discrete-state homogeneous Markov chain to model the stencil printing performance degradation process, and the quality loss during the stencil printing process is estimated based on this degradation model. A stencil cleaning decision model based on renewal reward theorem is established, and the optimal cleaning time is obtained through a balance between quality loss and the loss on idle time.

A stencil cleaning decision model for solder paste printing is established, and numerical simulation results show that there exists an optimal stencil cleaning time which minimizes the long-term loss.

Stencil cleaning control is very important for solder paste printing. However, there are very few studies focusing on stencil cleaning control. This research contributes to developing a model to optimize the stencil cleaning time in solder paste printing process.

This research aims to study the stencil printing process of the quad flat package (QFP) component with a pin pitch of 0.4 mm. After the optimization of the printing process, the desired inspection specification is determined to reduce the expected total process loss.

Static Taguchi parametric design is applied while considering the noise factors possibly affecting the printing quality in the production environment. The Taguchi quality loss function model is then proposed to evaluate the two types of inspection strategies.

The optimal parameter-level treatment for the solder paste printing process includes a squeegee pressure of 11 kg, a stencil snap-off of 0.14 mm, a cleaning frequency of the stencil once per printing and using an air gun after stencil wiping. The optimal upper and lower specification limits are 119.8 µm and 110.3 µm, respectively.

Noise factors in the production environment are considered to determine the optimal printing process. For specific components, the specification is established as a basis for subsequent processes or reworks.

Wafer-level stencil printing of a type-6 Pb-free SAC solder paste was statistically evaluated at 200 and 150 μm pitch using three different stencil manufacturing technologies: laser cutting, DC electroforming and micro-engineered electroforming. This investigation looks at stencil differences in printability, pitch resolution, maximum achievable bump height, print co-planarity, paste release efficiency, and cleaning frequency. The paper aims to discuss these issues.

In this paper, the authors present a statistical evaluation of the impact of stencil technology on type-6 tin-silver-copper paste printing. The authors concentrate on performances at 200 and 150 μm pitch of full array patterns. Key evaluated criteria include achievable reflowed bump heights, deposit co-planarity, paste release efficiency, and frequency of stencil cleaning. Box plots were used to graphically view print performance over a range of aperture sizes for the three stencil types.

Fabrication technologies significantly affect print performance where the micro-engineered electroformed stencil produced the highest bump deposits and the lowest bump height deviation. Second in performance was the conventional electroformed, followed by the laser-cut stencil. Comparisons between the first and fifth consecutive print demonstrated no need for stencil cleaning in the case for the micro-engineered stencil for all but the smallest spacings between apertures. High paste transfer efficiencies, i.e. above 85 per cent, were achieved with the micro-engineered stencil using low aperture area ratios of 0.5.

Stencil technology influences the maximum reflowed solder bump heights achievable, and bump co-planarity. To date, no statistical analysis comparing the impact of stencil technology for wafer-level bumping has been carried out for pitches of 200 μm and below. This paper gives new insight into how stencil technology impacts the print performance for fine pitch stencil printing. The volume of data collected for this investigation enabled detailed insight into the limitations of the printing process and as a result for suitable design guidelines to be developed. The finding also shows that the accepted industry guidelines on stencil design developed by the surface mount industry can be broken if the correct stencil technology is selected, thereby increasing the potential application areas of stencil printing.

SMT adhesives are applied to printed circuit boards by the following techniques: dispensing (c. 90% of all manufacturers use this technique at present), printing and pin transfer. The conventional dispensing method of applying adhesive utilises variations in dispense time, pressure and temperature combined with needle diameter to form deposits of varying volume and geometry. Recently, the printing technique has attracted a lot of interest. This technique is well known from solder paste printing. The major driving force is the higher throughput of this application method. moreover, a new printing technique with thick stencils allows the deposition of glue dots with different diameters and different heights. Two printing methods will be discussed: conventional printing technology and printing with thicker stencils.

A new range of non‐contact, non‐immersion stencil/screen cleaners has been launched by Surf Systems. The advent of new generation non‐CFC cleaning fluids for removal of solder paste residues from stencils, screens and mis‐registered boards has resulted in the SURF SS 1000 and 2000 spray cleaner Screenwash Systems. Designed to utilise a selection of processing fluids, the systems will not restrict production to a single cleaning product.

This paper aims to establish the predictive equations of height, area and volume of printed solder paste during solder paste stencil printing (SPSP) process in surface mount technology (SMT) to better understand the effect of process parameters on the printing quality.

An experiment plan is proposed based on the response surface method (RSM). Experiments with 30 different combinations of process parameters are performed using a solder paste printer. After printing, the volume, area and height of the printed SAC105 solder paste are measured by a solder paste inspection machine. Using RSM, the predictive equations associated with the printing parameters and the printing quality of the solder paste are formed.

The optimal printing parameters are 175.08 N printing pressure, 250 mm/s printing speed, 0.1 mm snap-off height and 15.7 mm/s stencil snap-off speed if the target height of solder paste is 100 µm. As the target printing area of solder paste is 1.1 mm × 1.3 mm, the optimized values of the printing parameters are 140.29 N, 100.52 mm/s, 0.63 mm and 20.25 mm/s. When both the target printing height and area are optimized together, the optimal values for the four parameters are 86.67 N, 225.76 mm/s, 0.15 mm and 1.82 mm/s.

A simple RSM-based experimental method is proposed to formulate the predictive polynomial equations for height, area and volume of printed solder paste in terms of important SPSP parameters. The predictive equation model can be applied to the actual SPSP process, allowing engineers to quickly predict the best printing parameters during parameter setting to improve production efficiency and quality.