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DVD Deterioration?
The author, Rohan Byrnes, can be contacted at rtbyrnesau@yahoo.com
Latest updates to this site
February 2, 2003: 'DVD rot' article in SMH - addressing some issues...
Yesterday (Feb 1) an article about 'DVD rot' was published in the Sydney Morning Herald newspaper. I was contacted for some comments regarding the issue, but in the end only two words from me made it into the finished article. Although the article is generally not too bad, there are some glaring problems I would like to take issue with.
1. Quote: "Unofficial estimates put the number of affected discs at between one and 10 per cent". I don't know where they got this from but it seems rather extraordinarilly high. If as the article later states that Australians purchased 13.3 million discs last year, then even at a rate of 1% this would imply there are 133,000 discs in Australia alone affected by DVD rot or delaminations!!! I'm sorry, but the figure is probably very much smaller than that. And it is because it is such a small problem that it is very difficult to convince some people that it is real.
2. The article makes the very good distinction between 'DVD rot' (which appears to be a rate controlled chemical attack of the aluminium coating, see below and in updates) and 'delamination' (which is a mechanical separation of the two layers by overstressing of the disc). However, it then goes on to imply (both in the main body of the article and in the photo caption) that the main cause of both types of failures are poorly designed cases. Poorly designed cases can indeed initiate a delamination at the centre hub of a dvd, however, they are in no way responsible for the microscopic spots I have observed in genuine 'DVD rot' cases (as detailed on this website).
3. Quote: "Rohan Byrnes, 34-year-old science fiction fanatic". Makes me sound like a loser. Maybe I am.....
4. Quote: "He works as a failure analysis engineer, with access to an optical microscope". This is fine (although it should perhaps read 'high-resolution optical microscope'). My issue is more with a comment online regarding this which read "Wow ... you can't just by (sic) that kind of technology in a high street store. No, wait, actually, you can...". Interesting comment considering the particular high-resolution optical microscope I am using costs about AUD$50,000 - perhaps somebody could confirm for me that you can walk into any high street store and pick one up....
5. The article refers to "glue" used to bond the two layers of a DVD together. This was not my term. The phrase I used was "liquid resin which is hardened to a strong bond using ultra-violet light", but I guess that doesn't make good copy! 
In summary, the phenomenons of 'DVD rot' and 'delamination', and the DVD manufacturing process, are quite complicated and unfortunately not something that can be covered adequately in a couple of hundred word article in a paper for the masses.
Thanks for listening.Rohan
September 25, 2002: "Planet of the Apes (1968)", Region 4
August 19, 2002: "Moonraker", Region 4
July 31, 2002: "Men In Black" Collector's Edition, Region 4
Introduction
Recently I was watching my region 4 DVD of the James Bond film "Thunderball" when, immediately after the layer change at the 88min mark, I began to notice some minor picture and sound break-ups. The minor break-ups continued for the next 2 minutes approximately. From then on until the end of the film the picture and sound were fine.
After the film had finished, I removed the disc and cleaned it by wiping the playback surface gently in a radial direction with a soft lint free cloth. I placed the disc back in my DVD player, cued it up to the layer change point and played it back again. Unfortunately the picture and sound problems were still present after the layer change. Fearing I had found my first case of so called "DVD rot", I decided to investigate the problem a bit further.
"Thunderball" Disc History
The "Thunderball" disc was purchased in September 2000 from a Kmart retail store. It was viewed once shortly after purchase by myself, and then a second time a few months later by a friend. On both occasions, neither of us noticed any corruption of the picture and sound during the entire film. Since then the disc has been kept in its original cover, stored on an ordinary bookcase in room temperatures ranging from approximately 15°C to 30°C, depending on the time of year. My repeat viewing, on 14th of July 2002, was the third playback of the disc and the first time any picture and sound problems were observed.
Visual Examination
The "Thunderball" DVD was examined visually for signs of gross defects such as delamination and heavy scratching. The disc was observed to be a uniform gold colour all over, with no observable discolouration or discontinuities present that might indicate a delamination. The playback surface was found to be in satisfactory condition, with only some minor dust particles present.
Optical Microscopy
The basic structure of a dual layer DVD disc is illustrated schematically in Figure 1. Fundamentally, starting from the playback side, the disc consists of data layer 1 (the first layer as played back by the DVD player), backed by a semi-reflective metallic coating (often gold). Behind this is data layer 2 (the second layer as played back by the DVD player), and a second reflective metallic coating (aluminium). Playback of a (reverse spiral) dual layer disc commences on the inner radius of the upper (first) layer and continues to the outer radius. The laser beam is then refocused to the outer radius of the lower (second) layer and then continues back in towards the inner radius. Since the problems with the "Thunderball" disc occurred immediately after the layer change, the examination concentrated on the outer edge of the disc and in particular on the reflective metallic coatings of the two layers. These areas are shown highlighted in Figure 1 with red lines (Areas 1, 2 and 3).
Figure 1. Basic structure of a dual layer DVD disc. The red lines indicate the areas this examination concentrated on i.e the top surface of layer 1 (Area 1); the semi-reflective metallic coating of layer 1 (Area 2) and the reflective metallic coating of layer 2 (Area 3). Drawing not to scale.
Examination of the upper surface of the first layer of the "Thunderball" DVD, at the approximate position of the layer change (i.e. Area 1, Figure 1), revealed the presence of minor particles of dirt and fibre, see Figure 2. The particles did not seem unusual for a 2 year old used disc.
Photo x70 approx.
Figure 2. Photograph of the top surface of layer 1 of the "Thunderball" DVD at the approximate position of the layer change. Note the presence of minor particles of dirt and fibre, typical for a used disc.
Maintaining the same location but focussing deeper into the disc and onto the semi-reflective coating of layer 1 (i.e. Area 2, Figure1), revealed the presence of fine grained metallic particles, see Figure 3. The particles of the metallic coating were uniform in size and density, with no observed defects present.
Photo x300 approx.
Figure 3. Photograph of the semi-reflective metallic coating of layer 1 of the "Thunderball" DVD at the approximate position of the layer change. The metallic coating appeared to be clean and in good condition, with a uniform particle size and distribution. Note the faint dark "splotches" in this image. These are something located below the semi-reflective layer, and hence out of focus in this image. See next figure.
Maintaining the same location again but focussing deeper into the disc and onto the reflective metallic coating of layer 2 (i.e. Area 3, Figure 1), revealed the presence of more fine grained metallic particles. The particles forming this coating were similar in size and distribution to those of the semi-reflective coating shown above. However, in this case many dark "spots" in the coating were also observed, see Figure 4.
Photo x300 approx.
Figure 4. Photograph of the reflective metallic coating of layer 2 of the "Thunderball" DVD at the approximate position of the layer change. The coating has a similar grainy appearance to the semi-reflective coating shown in Figure 3 above. However, note the presence of many "spots" within the coating. (These spots are the out of focus "splotches" observed in the previous figure).
Lowering the magnification, but still focusing on the reflective coating of layer 2, it was observed that the spots in the coating were concentrated in a concentric ring, approximately 1.5mm wide, adjacent to the outer edge of the disc, see Figure 5. This ring of spots was present around the entire circumference of the disc at this location.
Photo x70 approx.
Figure 5. Photograph of the reflective metallic coating of layer 2 of the "Thunderball" DVD at the approximate position of the layer change. At this lower magnification it can the seen that the spots within the coating are concentrated in a concentric ring around the disc, approximately 1.5mm wide. (Note: the larger, out of focus blobs are the dirt particles on the upper surface of the disc as shown in Figure 2).
A further photograph, Figure 6 below, shows the spots are located approximately 1.2mm in from the outermost edge of the reflective coating of layer 2. This is probably the region the DVD laser focuses on immediately after the layer change occurs (i.e. where the picture and sound problems observed on playback occurred).
Photo x70 approx.
Figure 6. A second photograph of the reflective coating of layer 2 of the "Thunderball" disc showing the location of the spots from the edge of the coating (approximately 1.2mm in from the edge).
Examination of the reflective coating of layer 2 of the "Thunderball" DVD at locations other than the edge where the layer change occurs, revealed the occasional random dark spot, but no other clusters like that observed in Figures 5 and 6. A similar survey of the semi-reflective coating of layer 1 did not reveal the presence of any spots at any location. Therefore it appears that the spots in this DVD are concentrated solely in the 1.5mm wide ring in the reflective coating of the second layer, adjacent to the outer edge of the disc.
Further Investigation
It is at this point that I decided I needed to survey some more dual layer discs. I selected five discs purchased over the last five years (one from each year), as follows:
"LA Confidential" Warner Brothers Region 4; purchased 1998 (previously reported as a 'problematic' title).
"The Matrix" Village Roadshow Region 4; purchased 1999.
"From Russia With Love" MGM (through Fox) Region 4; purchased 2000 (at the same time as "Thunderball").
"Live and Let Die" MGM (through Fox) Region 4; Purchased 2001.
"The Time Machine" Warner Brothers Region 4; Purchased 2002.
Each of these discs has previously played back for me with no picture or sound problems whatsoever. The five discs were subjected to the same optical microscopy examination as that of the "Thunderball" disc.
Figures 7 to 11 are photographs of the reflective coating of the second layers of the five discs listed above. "LA Confidential" is the only one to show the presence of the spots, see Figure 7. In this case however, they are concentrated at the very edge of the reflective coating and, qualitatively, there do not appear to be quite so many as there are on the "Thunderball" disc.
The reflective coatings of dual layer discs probably extend beyond the actual data of the disc. Therefore, in the case of "LA Confidential" the spots on the very edge of the disc are probably beyond the edge of the encoded data. This could explain why there are currently no visible signs of playback problems with this disc. Contrast this with the spots on the "Thunderball" disc which, being about 1.2mm inward of the extreme edge (Figure 6), probably fall within the data region of the disc and therefore could be upsetting the playback of this title.
Finally, in comparison, note the cleanliness of the reflective coatings of the second layers of the other four discs (Figures 8 through 11).
Photo x70 approx.
Figure 7. Photograph of the reflective metallic coating of layer 2 of the "LA Confidential" DVD. Note the presence of spots similar to the ones on the "Thunderball" DVD. However, in this case the spots are clustered at the very edge of the reflective coating (probably beyond the data region) and do not appear to be as concentrated as the ones on "Thunderball".
Photo x70 approx.
Figure 8. Photograph of the reflective metallic coating of layer 2 of the "Matrix" DVD. The coating on this DVD was free from spots.
Photo x70 approx.
Figure 9. Photograph of the reflective metallic coating of layer 2 of the "From Russia With Love" DVD. The coating on this DVD was also free from spots.
Photo x70 approx.
Figure 10. Photograph of the reflective metallic coating of layer 2 of the "Live and Let Die" DVD. The coating on this DVD was also free from spots.
Photo x70 approx.
Figure 11. Photograph of the reflective metallic coating of layer 2 of the "Time Machine" DVD. The coating on this DVD was also free from spots.
Questions Raised
What exactly are the "spots"?
How did the "spots" get there?
Were they there from 'day 1' or have they 'developed' over time?
Are the "spots" responsible for the picture break-ups that occur immediately after the layer change in my "Thunderball" DVD?
This last question is of particular interest. The DVD format has been designed with a high level of error correction built in. The hardware is supposed to be able to cope with linear defects up to 6mm long in the direction of the laser path. Is it possible that the shear number of these spots during this portion of my "Thunderball" DVD are causing cumulative read errors that exceed the error correction capabilities of the format, resulting in corrupt data being displayed on playback?
Contact Details
I am interested in discussing any aspects of the above with all interested parties. In particular I welcome feedback from any disc manufacturers or DVD industry professionals. I can be contacted at [email]mailto:rtbyrnesau@yahoo.com.[/email]
Thank you for taking the time to read this.
http://www.andraste.org/discfault/discfault.htm
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