Emerald Group Publishing Limited
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SMTA International Conference and Exhibition
SMTA International Conference and Exhibition
12-16 September 1999, San Jose Convention Centre, California
Keywords: SMART, SMTA, Conferences, Exhibitions
Flying into San Francisco International Airport and getting to San Jose is so easy, just a bus ride from directly outside the arrivals hall - what could be a simpler task? I must admit it would have been nice to avoid the work element of this trip and spend the weekend in one of my two favorite cities. Eating at the pier and watching the street artists at the tram terminus is great fun.
Well, back to work. When you first arrive at the exhibition centre it's time for a Kodak moment. The view below shows the less than impressive architecture of the convention halls with the ball fountains (Plate 1). Just after this shot was taken we bumped into our first SMART Group member from the UK and at 7.30a.m., on a Sunday, there is dedication. The American trade shows often have their seminar events start on a Sunday - it may be they are keen, want an opportunity to take the family away or there are special deals on weekend travel.
Plate 1Entrance to the SMTA International event in sunny San Jose, California
The SMI Conference program has long had the reputation of being an extremely good event where most of the best international speakers can be heard. In the case of this author they must have lowered the standards this year or needed an extra European. The workshop and seminar program ran from 12-16 September and were organised and produced by SMTA, the equivalent to The SMART Group in the USA; Nepcon ran the show along side the conference. Details of where to obtain the conference proceedings are given below and I would recommend purchase of a copy.
Sunday was dedicated to workshops given by some of the best names in the business, like Jennie Hwang (Plate 2); Automatic inspection using X-ray and optical techniques: Martin Wickham (Plate 3); and Armin Rhan.
Plate 2Jennie Hwang
It is not possible to look at all the papers presented at the conference, so let us look at a selection which would justify the expense of the proceedings and the rest would just be a bonus.
"Enhancing board level BGA assembly and reliability", by Steve Dunford, Raytheon Systems Company McKinney, Texas
The paper is basically a step through the whole process from board design, component goods in inspection to final inspection and test. It provides many of the key areas where problems can occur and is well illustrated with photographs. It is surprising how many subtle problems can still be found at goods receipt which we often miss. This presentation has also been more recently given at "Real World BGA/CSP Applications" by the SMTA during an exhibition in Dallas, Texas in October. "Thermogravimetric analysis predictions of reflow profiles of solder paste", by Charles Bradshaw and Quan Sheng, OMG Americas
Very interesting paper trying to take the black art out of what happens to solder paste during reflow. The thermogravimetric analysis has been used for a number of years to look at flux and paste formulations. Basically, a small sample of material is heated and the weight change of the sample is measured. This shows the change in the sample as various volatile materials are burned off.
Plate 3Martin Wickham
The purpose of the paper was to demonstrate how the results link to a temperature profile and the visual results on samples of reflowed paste. This seemed like a very practical way of viewing the process. The only criticism was that this does not take into consideration the effects of component mass. The printed paper in the proceedings did not have very clear reproductions of the graphs, so you would also need to talk directly to the supplier for additional information.
"Continuous improvement approaches for wave soldering process"
Having run wave solder training courses each month for the last ten years it is always interesting to see attempts to improve quality. This paper covered the use SPC, process monitoring, thermal profiling, in fact every technique to improve the process. The paper details the process used and the results obtained during the project and is ideal as a blueprint for any other company trying to improve yields on wave soldering.
One of the other benefits highlighted was on staff, the project raised the profile of the solder improvement team in the factory, which again would rub off on to other staff members to look more closely at their own process.
"A failure analysis and rework method on electroless Ni/immersion Au surface finish", by Zequun Mei, Hewlett Packard
The use of alternative finishes came to the fore six to eight years ago in an attempt to improve assembly yields. Nickel/gold was a particular favorite finish in Europe and the Far East, particularly for the cellular market. One issue which has plagued the industry has been the inconsistency of the nickel interface. When the nickel/gold finish is good it can last for a number of years, but when it's bad, find a bin!
The paper describes the possible failure modes of the finish and the results of testing conducted at the company. An interesting salvage process is also discussed for joints that have failed. This describes the cleaning of the nickel surface prior to resoldering.
The papers written by Nicholas Biunno of Hadco and the above text should be read by every engineer using this type of solder finish as they both provide an insight into the common failure modes seen in manufacture.
"Root cause failure mechanism for solder joint integrity of electroless nickel/immersion gold surface finishes", by Nicholas Biunno, Hadco Santa Clara, USA
This is a very well documented evaluation of the problems associated with poor solderability, poor wetting or simple joint failure. The evaluations conducted are well documented, easy to understand and very well illustrated with SEM, surface analysis and microsection views. The main conclusion from the work is that gold process attacks the surface of the nickel, causing the change in solderability. There are different levels of surface corrosion which will allow solder wetting to that which will not.
Corrosion has also been linked to selected pad and track configurations which build up a charge which in turn increases the corrosion effects. This is an issue which has been highlighted by other researchers looking at gold plating problems.
Organisation for the conference was handled by the SMTA team in their normal efficient manner (Plate 4).
Plate 4The SMTA team
Unfortunately, after my workshop presentations on Sunday and Monday morning it was back on a jet plane to host the OnBoard Seminars in London on Wednesday morning. Just no time for the wicked.
Copies of the complete SMI 1999 proceedings are available from SMTA Offices at Tel: 001612 920 7682; Fax: 001 612 926 1819; E-mail: firstname.lastname@example.org for price and availability.