Determining the Mechanical Characteristics of Gold Coatings on Conductive Traces in Printed Circuit Boards

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Nowadays, ever thinner coatings are being used in the electronics industry, not only to save material but also because of rapidly shrinking structure sizes. To reliably determine the mechanical characteristics of, for example, gold coatings with a thickness of only a few hundred nm, a precise and accurate measurement technique is required.

The thin Au coatings used on PCBs must serve various purposes: as corrosion protection, to improve solderability and to protect against wear. For detecting the mechanical characteristics of these thin coatings, such as hardness or elasticity, the instrumented indentation test is a well suited method with the further advantage of avoiding any influence of the substrate on the measurement results.

Mechanical Characteristics

Fig.1: Au-coated printed circuit board

For applications subject to mechanical stress, such as sliding contacts, the mechanical characteristics must exhibit absolutely non-varying parameters.

Figures 2 and 3 show the measurement results of two different gold coatings. Using the instrumented indentation test, a 0.5 µm Au coating was loaded with a test load of 0.2 mN and a 0.2 µm Au coating with a test load of just 0.05 mN.

The FISCHER PICODENTOR® HM500 measuring system is designed specifically to handle such small load parameters and travel distances. To better compare the results from the two samples, the time of the test load was adjusted so that the load increase curves both had the same slope.

Mechanical Characteristics

Fig.2: Schematic of a load-displacement curve including standard deviation of a 0.2 µm (red) and a 0.5 µm (blue) Au coating.

Mechanical Characteristics

 

Fig.3: Martens hardness (HM) including standard deviation of a 0.2 µm (red) and a 0.5 µm (blue) Au coating.

Both samples show nearly  identical hardness profiles (Fig. 3). Based on the standard deviation (variation coefficient of approx. 5%) one can clearly see how precisely these parameters can be determined, even for such thin coatings.

To precisely and accurately determine critical mechanical characteristics such as hardness and elasticity of even very thin gold coatings, FISCHER’s PICODENTOR® HM500 is the ideal instrument. For more information please contact your local FISCHER representative.

Mechanical Characteristics of Anodized Coatings

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In the automotive industry weight reduction – and the associated fuel savings – are top priority, which is why lightweight materials such as aluminium are used. In order to withstand mechanical stresses, however, these softer components must be made wear resistant. For this reason, hardcoat (Type III) anodization is becoming more common.

While  hard  anodized  coatings  are  typically  30-80  µm thick,  some  are  only  a  few  µm!  For  these  coatings, conventional hardness measurement systems that rely on  optical  evaluation  of  the  indentation  (e.g.  Vickers method)  approach  the  limits  of  their  ability.  A  much better method  is  the instrumented  indentation  test, which can be applied to measure not only the hardness in terms of plastic deformation (HV), but also to assess other   quality-determining   characteristics.   Using   the instrumented indentation test, even very thin anodized Depth [µm] coatings can be analyzed without risking influence from the substrate.

anodized coatings

Fig.1: Hard anodized piston

For such technical applications hard anodized coatings must have a consistent hardness of 400-600 HV across the entire section. Soft anodized coatings for decorative applications have a hardness of about 200-400 HV, which is reached a few hundred nm below the surface.

The FISCHERSCOPE® HM2000 with its ESP (Enhanced Stiffness Procedure) mode is able to determine mechanical properties like the Vickers hardness or the elastic indentation modulus dependent upon the depth.

Figure 2a/b shows the Vickers Hardness HV (calculated from the indentation hardness HIT) and the indentation modulus EIT of two coatings: a hard anodized coating (480 HV) of 11 µm thickness (shown in red) and a soft anodized coating of 14 µm thickness (shown in blue). The higher standard deviation for the hard anodized coating stems from the roughness of its surface.

anodized coatings

Fig.2a: derived data for Vickers hardness (HV) of a hard anodized (red) and a soft anodized (blue) coating

anodized coatings

Fig.2b: indentation modulus (EIT) of hard anodized (red) and a soft anodized (blue) coating

In Figure 2a one clearly sees the consistent hardness of the hard anodized coating and the increasing hardness of the softer anodized coating, which also exhibits less elasticity (Figure 2b, indentation modulus). On the hard anodized coating, the elasticity decreases as one approaches the substrate.

The FISCHERSCOPE® HM2000 is optimally suited for the precise determination of the mechanical characteristics of thin anodized coatings. Beside the hardness, other parameters such as the plastic or elastic material characteristics can be accurately assessed. Please contact your local FISCHER representative for further information.

Microhardness Tester for Quality Control of LCD Spacers

Two substrates, thin film transistor (TFT) arrays and colour filters, are common components of liquid crystal display (LCD) panels. Spacers are used to keep the gap between them consistent, so that the liquid crystal material can be injected evenly inside to “do its magic”. The mechanical properties of these spacers exert great influence on the finished display’s robustness and image quality.

The most common kinds of spacers used in TFT LCDs are bead (spherical) and column (patterned by lithogra- phy) type spacers. The collapse strength, recovery rate and height uniformity of those spacers play a major role in keeping the gap stable and, thus, the panel in good condition.

Strong spacers will keep the gap in good shape even under severe outside impact, while higher recovery rate means less permanent damage from those impacts. On the other hand, better height homogeneity of spacers will lead to faster response time, wider viewing angle, higher resolution and contrast ratio of the display. It is therefore important to monitor and control those parameters when manufacturing LCDs.

By compressing and releasing the spacers with the FISCHERSCOPE® HM2000 microhardness tester, these critical  mechanical  properties  can  be  precisely  meas-ured. For this purpose, a special indenter with a flat tip is used instead of the typical Vickers pyramid, as illustrated in Figure 2.

Fig. 2: SEM (scanning electron microscopy) image of bead spacer and the illustration of measurement with FISCHERSCOPE HM2000 and a flat indenter

Depending on the force applied to depress the spacer, different parameters can be monitored. With a relatively high force, the collapse strength of the spacer can be tested, while lower load levels are used to determine the recovery rate.

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Fig. 3a: Measurements on 10 bead spacers with max. load of 100 mN. The plateau indicates the collapse strength of the tested balls, while the vertical lines show spacer diameters.

Fig. 3b: Measurements on 10 bead spacers with max. load of 10 mN. The residual displacement divided by total displacement can be considered the recovery rate.

The FISCHERSCOPE® HM2000 is the ideal choice for measuring the mechanical properties of LCD spacers. Equipped with a flat-tip indenter, highly sensitive force control and displacement sensors, as well as a precise sample stage, the characteristics of each individual spacer can be determined in a single testing cycle. For further information please contact your local FISCHER representative.

Determining the Surface Hardness of Paint Coatings

Surface Hardness

Pencil Testing vs. Instrumented Indentation Testing

Until recently, quick scratch testing with pencils to determine the hardness of paint coatings has been commonplace. However, the reliability and reproducibility of this method is questionable. Because of the stringent quality standards in the coating industry, it is necessary to be able to test the hardness of paint coatings reliably.

Determining the ‘pencil hardness’ – or better put, the scratch resistance by means of marking with pencils – according to Wolff Wilborn or DIN ISO 15184 is a method commonly used in the coating industry. With this method, pencils of different hardnesses are moved at a certain angle and with a certain force across the paint surface to be tested. The ‘pencil hardness’ of the coating is defined by two consecutive levels of pencil hardness, where the softer one leaves only a writing track, while the harder one actually causes a tangible deformation of the paint coating.

Surface Hardness

Fig. 1: FISCHERSCOPE® HM2000 S for the determination of the Martens Hardness

The shortcomings of this procedure lie in the poor reproducibility of the measurements. For one,  the material under test will not always manifest the same properties, since pencil hardness is not clearly defined in any standard and there are distinct differences between individual manufacturers. Furthermore, the operator influence is significant. Thus, it is often impossible to interpret the results unambiguously.

Surface Hardness

Fig. 2: Comparison of the Martens Hardness of pencils of different hardnesses, shown with the standard deviation of the measurements

If one correlates the various pencil hardnesses with their Martens Hardness, the limitations of the method become even more obvious. Fig. 2 shows the results of multiple measurements on  pencils  of various hardness  levels. Broad overlapping is apparent when one considers the standard deviations of the individual test series. In fact, especially in the upper range, the nominal hardness (B, HB, F, H, etc.) of pencils is not a dependable indicator of their actual hardness.

The FISCHERSCOPE® HM2000 S can measure the hardness of paint coatings directly and accurately. In addition, other characteristics can be determined, such as creep and relaxation behavior, as well as the modulus of elasticity. All of these hardness parameters provide a true indication of the paint quality.

FISCHERSCOPE® hardness measurement systems demonstrate that the actual hardness of a pencil can vary significantly from its nominal hardness, meaning the pencil is not a dependable measuring device. Therefore, a method employing a pencil as its key instrument cannot be expected to reliably assess the hardness of anything. For directly determining  the  surface  hardness  of  e.g.  paint coatings, the FISCHERSCOPE® HM2000 S, for example, will give you the same accurate, precise results – every time. Contact FISCHER for more info (860)683-0781 or info@fischer-technology.com.

Mechanical Characterization of Lacquer Coatings in Automotive Applications

Lacquer Coatings

In the automotive industry lacquer coatings are used as protection from corrosion and external damage. These lacquers are exposed to environmental influences such as extreme temperature fluctuations or moisture and salt. In addition, automotive coatings must exhibit a certain toughness to make them resistant to stone chips and scratches, for example in car washes. This requires the right balances between hardness and elasticity.

Car paint has to fulfill different functions and therefore possesses various properties. A quick differentiation and determination  of  its  properties  is  possible  with  the characteristic parameters obtained from the instrumented indentation test:
The Martens hardness (HM) and the Martens hardness after creeping (HMCR) are values which specify plastic and elastic properties of the paint coating. The indentation hardness (HIT) considers only the plastic portion of the material deformation. The hardness parameters provide conclusions about aging, curing, cross-linking, embrittlement through UV radiation, hardness change through temperature influences  and the degree of polymerization of the lacquer.

Lacquer Coatings

Fig. 1: Weathering rack in Florida of the company Atlas with various car body parts

One of the most important advantages of the instrumented indentation test is the determination of elastic properties. Parameters like the modulus of indentation (EIT), elastic recovery (IT), creep at maximum load (CIT 1) and creep at minimum load (CIT 2) can be detected using this method. The parameters described above allow various conclusions regarding visco-elastic properties of lacquer coatings. These in turn show the vulnerability of the lacquer against weather influences, its susceptibility to rockfall, the ability to heal in case of scratches and the reflow behavior.

Sample HM

N/mm²

IT

%

C IT 1

%

C IT 2

%

E IT

kN/mm²

A (mean) 42.9 23.4 18.4 -10.6 1,39
(standard dev.) 1.2 0.8 0.2 0.3 0.1
B (mean) 143.0 45.7 6.1 – 9.0 3,07
(standard dev.) 5.6 0.4 0.1 0.3 0.1

Lacquer Coatings

Fig. 2: Martens hardness plot and plastic and elastic measurement parameters for 2K automotive repair paints; A being a soft sample and B a hard one

Using  the  FISCHERSCOPE®    HM2000  makes  the determination of material characteristics like surface hardness, cross-linking, elastic modulus and healing behavior in case of scratches simple and easy. In this manner, several chemical process parameters can be determined quickly during manufacturing or hardening of automotive paint coatings. Contact FISCHER  for  more  information:  (860)683-0781 info@fischer-technology.com.

Microhardness Measurements of Paint Coatings Shorten Weathering Tests

Microhardness Measurements

Paint for architectural coatings is not only used to give surfaces an attractive appearance, but also plays a very important role in protecting facades against external damage and corrosion. To avoid waiting years to see if the coating really protects the surface, simulating and measuring weathering influences is necessary.

Paint coating systems are exposed to severe environmental influences like strong temperature variations, moisture and aggressive media such as acid rain, insect residue or strong cleaning agents. Facade coatings should withstand such influences and have quality characteristics such as light fastness, weathering resistance and easy cleaning.

Microhardness Measurements

Fig. 1: Facade of a building with polyester powder coating.

The characteristics of such coatings depend not only on the thickness, but also on hardness, elasticity, degree of polymerization and resistance to UV radiation. These parameters can be determined using the instrumented indentation test. To demonstrate weathering influences, measurements were performed on samples with original surfaces (reference),  on  samples  after  400  hours  of  QUV

radiation (equipment weathering) and after 1 year Florida exposure test (outdoor weathering).

Microhardness Measurements

Fig. 2: Influence of weathering on the Martens Hardness of polyester powder coating.

The reference sample (green plot) without weathering does not show a hardness increase at the surface. The sample exposed to weathering outdoors for 1 year in Florida shows a slight increase of hardness near the surface. The sample exposed to QUV irradiation for 400 hours shows the largest hardness gradients. Reason therefore is a change in the molecular structure of the paint. Cross-linking of the paint molecules lead to an increase in hardness caused by the repeated alternation of drying, moistening and irradiation. As outdoor weathering often spans a number of years and involves very expensive sample holders and large standing areas, artificial weathering is used to simulate such outdoor weathering.

With the FISCHERSCOPE® HM2000 hardness measuring instrument, the effects of weathering tests can be measured easily and accurately, therefore saving costs  and  shortening  time  compared  to  outdoor testing significantly. For more information contact FISCHER (860)683-0781 info@fischer-technology.com

Hardness Measurement of Nano Coatings on Eyeglass Lenses

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Whether used for eye protection or vision correction, plastic eyeglass lenses are preferred over  glass  for  their  considerably  lower weight  and  better  fracture  strength.  In order to provide the required life-long quality of such lenses a specific scratch-resistance is necessary. This scratch-resistance can be determined through hardness measurement.

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Fig.  1:  Scratch-resistant  protective  coatings  are  essential  for  plastic lenses (picture courtesy of Rodenstock)

Current   eyeglass   lenses   made   of   plastic   are commonly  provided  with  an  anti-scratch,  dirt-repellent and  anti-reflective  surface.  They  are  vacuum  coated using a physical vapour deposition (PVD) method with up to 10 protective layers, each only a few nanometres thick,   which   together   ensure   very   high   scratch- resistance.  Hardness  and  scratch-resistance  of  these coatings are directly related: therefore, determining the hardness is a suitable method for quantifying the quality of these protective coatings.

To avoid commingling the hardness results of the coatings with those of the base materials while measur- ing, the test load must be absolutely minimal, as low as

a few micronewtons: The indenter may only penetrate up to one  tenth of  the overall coating depth  in order  to correctly determine its hardness without being influenced by the properties of the substrate (Bückle’s-Rule).

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Fig. 2: Hardness measurement of protective coatings of lenses (Martens hardness). Sample P4 has a significantly lower hardness and was identified as far less scratch-resistant (samples courtesy of Rodenstock)

Another important measuring parameter is the elastic/plastic deformation ratio of the coating material. The coatings must have a very high elastic component to prevent separation from the base material upon deformation. Therefore, multilayer coating systems are used that gradually adjust the modulus of elasticity from the base material to the top coating. These systems also have much higher adhesive bond strengths compared to single-layer coatings.

To secure the functionality of these protective coatings it is important to find the right balance between hardness and elastic behavior.

The PICODENTOR® HM500 is ideal for measuring the hardness and elastic properties of these complex, nano-thin multi-coatings, which requires a measuring system capable of load generation as low as a few micronewtons and highly accurate depth measurement in the picometre range – exactly the designed operating range of the PICODENTOR®. The hardness can then be calculated from the measured load/depth curves. For further info contact FISCHER (860)683-0781 or info@fischer-technology.com

Hardness of Complex Coating Systems for Optical Components

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The demands placed on the performance of optical components have skyrocketed and, in response, highly complex coating systems have been developed to produce surfaces that are scratch- resistant, dirt-repellent, anti-static and reflective. Various curing processes are integral to the production of optical coatings, making it difficult but important to find the decisive balance between coating hardness and elasticity.

Quality control therefore requires correspondingly powerful measurement methods and systems. For the standard-compliant determination of such material parameters as hardness and elastic modulus the instrumented indentation test can be used, even thin coatings of less than 100 nanometres in thickness can be measured accurately.

With the load/indentation depth method according to DIN EN ISO 14577 and ASTM E 2546, the indenter, typically a Vickers or Berkovich pyramid is pressed with continuously increasing test load into the material and then reduced in the same manner while simultaneously measuring the respective indentation depths. Important technological characteristics can be calculated from the resultant load/unload cycle, for example the Martens hardness. The elastic modulus of indentation can be determined when the test load is reduced.

Fischer Micro Hardness

Fig. 1: Depth-dependent profile of the Martens hardness (HM) of two differently composed optical coatings. Marked in blue is the area where already an influence from the base material is given according to Bückle’s rule.

The figure 1 presents the measurement of Martens hardness and the associated standard deviation on two plastic lenses, samples courtesy of Rodenstock GmbH, Munich. The samples were produced under the same process conditions but exhibit differences in the composition of the coating system. As result a significant change of the hardness from one coating to the other can be seen.

At a certain indentation depth, the substrate material starts to become detectible. In order to avoid that influence while measuring the coating, the indentation depth must be limited to no more than 1/10 of the coating thickness (Bückle’s Rule). The coefficients of variation for the two samples, 1.73 and 1.60 percent, respectively, as achieved using the FISCHER PICODENTOR HM500, demonstrates the potential for accuracy.

Complex Hardness Coatings

Fig. 2: The principle of instrumented indentation test: a designates the load increase, b the load decrease.

Although only the Martens hardness can be measured depth-dependent using standard methods, additional mechanical properties such as the Vickers hardness or the elastic modulus of indentation can be determined via the ESP (Enhanced Stiffness Procedure) method, which employs partial loading and unloading.

Conclusion: If the right balance between coating hardness and elasticity for coatings on optical components  has  to  be  determined  the FISCHER PICODENTOR® HM500 is the suitable instrument to evaluate these parameters. For more info please contact us: (860)683-0781 info@fischer-technology.com