Embossing tools for high-resolution manufacturing

Citation

(2008), "Embossing tools for high-resolution manufacturing", Soldering & Surface Mount Technology, Vol. 20 No. 4. https://doi.org/10.1108/ssmt.2008.21920dab.008

Embossing tools for high-resolution manufacturing

Article Type: Industry news From: Soldering & Surface Mount Technology, Volume 20, Issue 4

Exploiting its established expertise in Photo Electro Forming (PEF), Tecan has developed techniques to produce versatile cost-efficient embossing tools from which manufacturers can produce high-resolution prototype and mass-production parts in a range of materials.

Typical applications for embossing tools include refractive and defractive micro-lens arrays, optical components, microfluidic structures for medical and laboratory applications, and high-definition electronic / opto-electronic circuits.

The company can replicate originals produced in photoresist, etched silicon, glass and diamond-turned metal, typically to produce an exact mirror-image replica in nickel. For example, if the original is male or female, defined by the peaks and troughs of its profile, the nickel replica will be the opposite gender.

The process allows the nickel duplicate to be simply separated from the master and used for processing, as it is, or as a parent part from which mirror-image “offspring” can be produced, these will have exactly the same form and gender as the original. This allows expensive originals to be kept as perfect masters, from which any number of replicas, in any gender, can be produced at any time and at comparatively low cost – facilitating any level of production volumes of micro-featured parts.

Customised “master” embossing tools can also be produced from original engineering drawings using PEF – the master tool being “grown” into a photolithographically defined resist mould to create the original features required.

High aspect ratios are also possible – depending on the packing density of the part’s surface features – with ratios of up to 12:1 achievable.

The company can tailor its process to suit individual requirements utilising a broad range of photoresist chemistries. Tools can be produced up to 300 mm × 300 mm, with apertures sizes down to 2 μ, and alignment accuracy of less than 1 μ.

For further information, please visit the web site: www.tecan.co.uk

Design the problem out — before it costs you

Two instances of expensive reworking, related below, could have been avoided had the designers and manufacturing personnel applied Design for Manufacture (DFM) procedures, explains Eric Hinsley, Senior Tutor at Electronics Yorkshire.

Electronics Yorkshire is a not for profit organisation created to support the development of the Electronics Industry in the Yorkshire and Humber region as well as being a resource that assists clients and members outside the region who make use of the expertise at its Leeds centre.

Electronics Yorkshire has some very impressive equipment which members use to check and test their manufacturing processes and, it is obvious that even though people may have been in the industry for many years, they still need to extend their knowledge with the new technologies coming through. This is especially so with regards to the correct use of standards, to ensure higher yield for profit and lower rework costs.

Open circuit

The first company was having problems with high failure rate on test. This was due to an open circuit connection under a QFN (Quad Flat Pack, no leads) which was fitted to a highly populated PCB. Using the X-Tec Revolution X-ray equipment at Electronics Yorkshire it was established that some of the contact areas had none, or very little, solder on and, on further investigation, it was found that the solder had in fact “wicked” its way onto the nearest surface mount device (SMD) as this was too close (Figure 1).

Figure 1 Showing solder problems

The SMDs were not placed on the next batch when reflowed but instead were placed by hand on completion of the reflow process, which resolved the failure rate. The company had a lot of faulty PCBs that required the QFN to be replaced and several methods were tried, without success.

The company sought advice from Electronics Yorkshire who proposed using a dispenser to apply a volumetric amount of solder paste to the component pads, which was then reflowed, and then the QFN was placed using the Centre’s IR rework/repair machine (Figure 2 for the final result).

Figure 2 After final process

Scrapped components

The second company wanted to use a SMD connector for “hot swapping” equipment in the field. The contract stated only 10 per cent voiding in the solder connection was acceptable. A coupon was run through the reflow with a thermocouple drilled into the PCB at a connection site for a solder connection and the time/temperature profile was changed accordingly, so that a reading of 217°C was reached at the solder connection.

As can be seen from the X-ray image of Figure 3, there is a lot of voiding from the centre of each connection. On examination of the connector it was found that the centre of each connection was domed which would trap air when placed onto the solder paste of each connection and thus expand and outgas during the reflow process causing excessive voiding.

Figure 3 Showing the large outgassing

Soldering each of the connections first was proposed, then hand placing the connectors on to the solder paste on the PCB before reflow soldering. Although this did reduce the voiding to an acceptable limit (Figure 4), there were a few alignment issues on some of the PCBs which had to be scrapped to comply with the contract.

Figure 4 Final process

It was also seen from the X-ray image, that one of the connections did not appear to be correct, so a visual inspection was carried out using one of the Centre’s Ersascopes (Figure 5). It emerged that the same dispenser was used for solder paste as well as for the SMD staking adhesive and, clearly, it had not been cleaned properly during the changeover. The PCB could not be reworked and, again, had to be scrapped in compliance with the contract.

Although neither of these problems was complex, each had to have an extra process incorporated to complete the final product and meet the deadlines for output and customer requirements. The problems could not have been resolved quickly and easily without the experience of the operators and appropriate equipment, such as that used within the Electronics Yorkshire Centre.

However, the main issue was in the failure of the basic design. The faults only showed on manufacture, which is usually the case from prototype; hence the importance of Design for Manufacture (DFM) process.

Further information on the resources, facilities and equipment available for companies to use is available on the company’s website: www.electronicsyorkshire.org.uk.

Electronics Yorkshire is a not for profit organisation supported by the regional development agency, Yorkshire Forward, the Learning and Skills Council and European Union ERDF and ESF.

Figure 5 Side view of a connection