Tag Archives: epoxy adhesive

What is the Strength of Epoxy?

When trying to determine the strength of epoxy it is important to know what type of strength you need. When reviewing data sheets, one can get inundated with different strength values. On the other hand may only give one kind of strength. It is valuable to know the differences in the given values as well as what is important to your application. When it comes to epoxy adhesives and potting compounds, there are several important strength values. These values include shear strength, compressive strength, flexural strength, and peel strength among others.

Shear Strength

Shear strength, in regards to epoxy adhesives, are common values used to portray the strength of epoxy. The most common of the shear strength values is lap shear strength. Lap shear strength is tested using ASTM method D1002. This method calls for a single lap joint bonded with an adhesive on standardized aluminum. This test allows for the lap shear strength of an epoxy standardized to aluminum. It is an excellent value to compare adhesives against each other.

Lap shear strength tested on etched aluminum. Strength is determined by the maximum load force needed to break the bond created by the adhesive. Because the bond area is 0.5in2, the load force is doubled to calculate the lap shear strength typically given in pounds per square inch (psi).

 

The lap shear strength test not only determines the strength of the epoxy but also the mode of failure is an important factor. There are two types of failure modes: adhesive failure and cohesive failure. Adhesive failure results in the adhesive completely losing its bond to the substrate. Adhesive failure results in one panel without adhesive and the other with the entire adhesive. With a cohesive failure, the strength of the adhesive itself is not as great as the forces applied to it and the adhesive pulls apart leaving portions of the adhesive bonded to both substrates.

Typical values of lap shear strength vary, however high strength can be considered a product with a lap shear strength of over 2500psi. High lap shear strength epoxy adhesives from Epoxyset include EB-260, EB-316M, EB-127TC, and EB-135.

Die shear strength is an important value in the semiconductor industry. It is used to determine the strength of a die bonded to a package substrate using a die attach adhesive. The die is subjected to a stress parallel to the substrate. This causes stress at the interface between the die and the die attach material. The force needed to break the bond is the die shear strength. A high die shear strength is >3400 psi (10kg). Many of our semiconductor adhesives used in electronic assembly exhibit very high die shear strength. These products include our EO-24, EO-30M-1, and EB-470.

Compressive Strength of Epoxy

The compressive strength is the ability for the epoxy to handle weight. This test consists of applying force on the top and bottom of a cylinder of epoxy.

compressive strength

Compressive strength of an epoxy is important if the epoxy will be under heavy loads or under a high amount of weight. A typical compressive strength value for epoxies is about 10,000psi. Specially formulated epoxy materials, such as our EC-1850FT and EC-1850FT-LV, have compressive strength values of over 25,000psi. To put into perspective the compressive strength of the highest quality concrete is 5,000psi.

Flexural Strength

Flexural strength, also known as bend strength, is the material’s ability to resists deformation (or rapture) under a load. A bar of epoxy (or any material) is supported on the sides while a load pressure is applied to the middle. The amount of load the epoxy can withstand before fracture or deformation is the flexural strength.

flexural strength

Peel Strength

The peel strength of an adhesive is another type of strength of an adhesive bond. It is the average load per unit width of bond line required to part bonded materials where the angle of separation is 180 degrees and separation rate is 6 in/min. Generally very high peel strength adhesives have excellent bond to the substrates while having a lower modulus than most epoxy adhesives. A semi-flexible adhesive that bonds well tends to have the highest peel strength. This is because as the pressure is pulls substrates apart, the adhesive is flexible enough to withstand cracking.

peel strength

Epoxyset has a number of high peel strength adhesives designed for high bond strength and crack resistance. These products include EB-260, EB-316M, EB-116, and EB-127TC. These toughened epoxy adhesives are used in a variety of applications for the aerospace, medical, and industrial markets.

 

 

 

Underfill: Epoxy underfill for CSP and BGA

OEMs face ever-growing requirements for greater chip functionality, reduced size, mechanical toughness, and high reliability. As market trends that drive greater functionality, reliability, and ruggedness, the consumer demand for handheld, mobile, and portable systems, such as smart phones and tablets increase daily. In the military and aerospace industries portable electronics such as satellite, drones, GPS, and man packs represent a growing need for high reliability electronics in extreme conditions.

Ball Grid Array (BGA) and chip scale packaging (CSP) are common solutions for many of these problems however; other problems arise in using these techniques. Common processing problems include extremely short solder joints and thermal stress release.

Underfill for CSP and BGA

An underfill is a polymer applied on the PCB after it has been subjected to reflow. Underfills are typically epoxies however urethanes are also used. Underfills encapsulate the bottom side of the silicone chip protecting the fragile connections made from the bottom of the silicone chip and top of the PCB. Using underfills on BGAs and CSP produces enhanced mechanical and thermal properties.

Underfill

 

Underfills are typically dispensed on the corners or around the edge of the BGA/SCP which are then (on the PCB) heated so the underfill can absorb to under the chip. Typically it is heated to 120-165°C. The temperature remains until the polymer is completely cured. The whole process takes anywhere from 5 minutes to over an hour depending on the polymer. More resilient underfills can take longer to cure and to reduce shrinkage during cure.

Underfill polymers are becoming more and more popular because it solves many problems associated with smaller form factors. It provides extra rigidity with strong mechanical bonding between chip and the PCB’s corresponding connection, thus protecting solder joints from mechanical stress. Thermally conductive epoxy used as underfills help transfer heat away from highly complex, high power chips. Many low expansion underfills have very low coefficients of thermal expansion (CTE) and can help smaller packaging during thermal cycling. Also, instead of stress only on the roots of the solder balls undefills allow for stress relief across the whole package. Underfill also greatly improves the high-gravitational acceleration (High-G) performance, thermal-cycle performance, and fatigue cycle performance.

Certain harsh environmental forces may deal a particular blow to a device’s solder bonds, damaging solder connections. This is especially true when using a combination of micro-BGAs and micro-CSPs and high reliability requirements. Using undefill epoxy the strength of the connections can multiply 10 fold. The underfill process dramatically enhances thermal-cycling performance and shock resistance of those chip packaging and board connections.

The PCB designers and assembly engineers work together closely to determine the right undefill, amount, and properties are used. Many times, the CTE is the most important property when evaluating underfill systems. Many highly filled epoxy underfill products have a CTE of below 30ppm/°C below glass transition temperature (Tg). These same systems have a Tg of above 120°C and as high as 160°C. Epoxyset’s EC-M22LV-1 is an example of a highly filled, rigid epoxy undefill.

Another type of underfill are low modulus underfill systems. These tend to be high CTE and lower Tg however the lower modulus allows the better absorption of mismatch between the board and chip. Low modulus underfill systems generally tend to be flexible urethane or epoxy systems. EPOXIBOND EB-109M-4 is an unfilled, low modulus undefill that has excellent capillary action for easy application. A urethane option is UB-55 or UB-70. These 2 products are low modulus and use sustainable raw materials.

Uncategorized

Epoxyset Adhesive Solutions for Ultrasound Technology

Epoxyset Adhesive Solutions for Ultrasound Technology

July 31st, 2014

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For over 15 years, Epoxyset has been formulating and producing many types of high performance adhesives and polymers used in ultrasound technology. Ultrasound technology is not just limited to medical applications such as interior body screening. It is also used in the oil and gas industry for measuring motion and flow, the exploration industry for sensing and measuring, and also consumer electronics such as speakerphone and microphone components.

Basic principle of medical ultrasonic probes (transducer)

The ultrasonic probe consists of a piezoelectric element, backing material, an acoustic matching layer and an acoustic lens. The following describes the components and their functions of the convex type probe as an example:

Epoxyset, as an advanced adhesive manufacturer, applies its proprietary technologies to the probe manufacturing processes, such as formulating and producing backing layer elements and bonding of acoustic matching layers as well as innovative acoustic lens material.

Piezoelectric Element (PZT)

The piezoelectric element (PZT) is the part of the transducer that generates ultrasonic waves. On both sides of the PZT element electrodes are affixed and a voltage is applied. The element generates a sound wave by oscillating due to repeated expansion and contraction. When the element is externally applied with vibration (or an ultrasonic wave) in turn, it generates a voltage.

 

 Ultrasound tech

(http://www.ndk.com/en/sensor/ultrasonic/basic02.html)

 Function of the backing material

The function of the backing material is to reduce and/or prevent excess vibration of the piezoelectric element. The backing material is located directly behind the PZT element. By reducing excessive vibration will cause the element to generate ultrasonic waves with a shorter pulse length, improving resolution in images. Epoxyset produces a number of backing materials for various transducer manufacturers. Working closely with these companies, Epoxyset utilizes different polymers, additives, fillers, and curing agents to deliver a backing layer suitable for the need of the transducer.

 

Function of the Matching Material

Ultrasonic waves transmitted from the PZT element are reflected off a target because there is a big difference in acoustic impedance between the piezoelectric element and the object. To avoid this, an intermediate layer is (matching layer) is added between the two so that ultrasonic waves can efficiently enter the object. It is not uncommon to have several different matching layers in a single transducer to gradually decrease impedance between the PZT element and the object. Epoxyset offers acoustic matching layers to have adequate acoustic impedance value using a combination of different resin materials, fillers, and additives. It is important to deliver a product that not only offers the appropriate acoustic properties but also is easily processed and applied.

 

Function of the acoustic lens

The acoustic lens is the outer layer most people see when they look at an ultrasound transducer. It is usually grey or black or green and looks like a rubber attached to the end of the probe. Ultrasonic waves transmitted from the probe would spread and travel like light. The acoustic lens prevents the ultrasonic waves from spreading and focuses them in the slice direction to improve the resolution.

When the probe emits ultrasonic waves, they would travel like light and spread in all possible directions without a lens. The acoustic lens prevents the ultrasonic waves from spreading and focuses them in the slice direction to improve the resolution. On many probes, the lens material is usually a commercially available silicone adhesive. However, for higher sensitivity probes silicones are not acoustically viable. Epoxyset develops new and innovative lens and window castings for high sensitivity probes using proprietary polyurethane chemistry.

Recent-news

EB-106

EB-106

April 5th, 2014

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EPOXIBOND EB-106 is a low viscosity, optically clear, epoxy adhesive. With a pot life of 1 hour, this product is ideal for bonding, small potting and encapsulation, and coatings for the optical and fiber-optics industries. It exhibits very high bond strength to several substrates including a variety of metals, glass, ceramics, wood, PCBs, and several…

Featured Products

EB-135

EB-135

March 27th, 2014

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EPOXIBOND EB-135 is a medical grade, low viscosity, optically clear epoxy adhesive. It is used in various industries including medical device manufacturing, optical and fiber optics, aerospace, and electronics. As a high temperature adhesive, EB-135 can be used continuously at temperatures of up to 150°C. It is also specially formulated to be used in easy to use 2:1 dual cartridges. Common applications include bonding metals, ceramics, glass, wood, and even some plastics. EB-135 can also be used to pot and encapsulate small electronic components, create air tight seals, and as a chemically resistant coating.