Jim, I revisited Diskcon today and I focused more on head interconnect technologies.|
Tuesday, I tried to explain what I thought were the differences between TSA and CAPS which are laminated circuits versus flex circuits like those from Innovex, 3M and Read Rite's Rite Flex unit. Just to get the words right, they often call these flex circuits FOS or Flex on Suspension.
Well, I made some mistakes. I'll probably make more mistakes, but this is a discussion forum and I hope anyone will chime in and correct me where they can.
Earlier, I said I thought the main differences between TSA and FOS was the stainless steel base. Well, this is true, but what I didn't realize was the stainless steel base becomes the Flexure. This is important as there must be a flexure. Not having a base, means FOS must be bonded to a flexure where TSA and CAPS are the flexure.
To explain again, a suspension has 3 main parts; the base which has a big hole in it and is the main attachment point to the head stack; the load beam holds the flexure and head out over the rotating disk; and finally the flexure where the head is attached.
A flexure must flex as it implies. It is affected by air as the disk spins. It must flex in a very precise, predictable manor. Precision is all the more necessary now that heads are smaller and more sensitive. So, the main argument against FOS is that it carries extra weight onto the Flexure. More weight on the flexure means it has to be stronger and heavier. That goes against the goal of a flexure. Please correct me if I am wrong.
I think my earlier description of CAPS is still more or less correct. The difference between TSA and CAPS is how they make the copper circuit. CAPS is an additive process of sputtering copper (CAPS). TSA is a subtractive process of etching a circuits out of a layer of copper. Today, I learned CAPS is said to offer finer line widths, sub .25 microns. TSA can't make as fine line widths at this time. I think the TSA minimum is .5 microns.
FOS is also a sputtered process, which offers finer line widths. FOS is sputtered in liquid, CAPS is sputtered in a vacuum. Innovex says this is a harder process to manage and more costly.
Again, weight on the flexure. CAPS is said to weigh less than TSA because of these finer lines. How much of a difference can this really make? If this seemingly incredibly small difference is important, I can see claims about FOS are justified. Well, one thing is sure. There are a lot of opinions. You can be sure that this issue is not lost on Innovex, 3M and Rite-Flex, not to mention Seagate who is the most aggressive adopter of FOS. Isn't this interesting. Who is right?
Now, if you thought things were simple so far, I found yet another TSA like laminated circuit called CIS. It is made by Nitto Denko. They work with NHK, another suspension maker. They are both Japanese companies. CIS seems to be a more or less a CAPS like design using a metal base and sputtered copper lines. CIS is being used in drives by Quantum on NHK suspensions.
So that makes at least 6 companies competing for head interconnects. Here we thought it was more or less a race between Hutchinson and Innovex. I'd bet IBM probably also has an in-house version.
There's more to this story yet. Older paired wires were long enough to make connections that ran deep into the drive making the interconnect from the head to brains of the drive. Currently, TSA, CAPS and CIS end at the base. A bridge using a flex circuit is needed to complete to connection. So, here is a new market for bridge circuits. They cost about .40 and they are not simple to make or attach. All 3 FOS makers will compete for this job.
A possible solution is to make the TSA longer using what's called a tail. Tails complicate the process of making the laminated circuit and add a lot more cost. Tails are said to be fairly easy and cheap for FOS. So, again you have a cost trade off. We need to get exact figures on how much more a TSA with tail costs, but I am told it's greater than .40. A tail only adds another 2 or 3 inches to TSA, but cuts the amount of parts that can be processed in a batch.
Currently Innovex sells bridge circuits to Maxtor among others. Innovex says this is a high margin product that is also very attractive to make, so they could win even if they loose.