Application Note 44 - SCSI Drives and Connectors

Application Note 44 - SCSI Drives and Connectors

Background
SCSI drives are used both in multi-channel sound recording (where they replace tape drives) and in digital recording as used in animation. In either case, they allow the digital recording to be removed. At a later time, it can be edited or copies made, edited and assembled. One possible problem occurs as the SCSI drives themselves are in removable caddies. At one time, SCSI 2 was most frequently employed (50 pin connectors) but with speed and resolution increases, the need for SCSI 3 (with 68 on connectors) is now almost standard.

Now, even SCSI 2 and SCSI 3, may have die cast bodies. The need for larger hard disk storage mandated the use of SCSI 3, as twelve SCSI drives can be employed. As these connectors are smaller than the SCSI 1, their pin spacing is smaller. But where larger arrays are involved, these are usually plugged into a back plane by using a single unified 80 pin connector.

This technique is termed SCA connection. With a pin density this extreme, cable and pin connection become very dependent on anything that can cause a conductivity error. Rectification of RF signals where the signal voltages are low and the circuit impedance is high can result in the proliferation of errors.

Connector problems
It is rare that connector faults show up immediately. But when the 68 pin caddies or removable SCA 80 pin drives are used, errors can accumulate until "best two out of three" becomes one "out of three" This situation is rare; which drive is correct?

Note that the use of the RAID technique allows for "hot swapping". In essence this means that defective SCA drive can be replaced without powering down the system.

As the larger storage systems use error correction (best two out of three) in a RAID configuration (Redundant Arrays or Inexpensive Drives), it isn't until two of the records are faulty that a major problem becomes apparent. But in some cases they may often be of an intermittent nature and thus difficult to trace. Stabilants can be used to prevent or solve these problems. We'll explain the use of this material in some detail.

images for SCSI 1, 2 and 3 
	connectors
Connectors for SCSI 1, SCSI 2 and SCSI 3

On some connectors, the metal may be tin plated; with several sets of gold flashings applied after the tin plated connector is formed. However, when a connector's stock is tin plated before it is formed one must remember that some tin alloys resist high-speed forming and can have areas of latent stress. Whenever this type of connector is subject to thermal stress and/or cycling of humidity, the pre-stressed tin may "flake" away. These "flakes" are so small that micro-techniques have to be used even to see them. We have encountered instances where connectors passed quality control testing and were approved for shipping. Often these connectors were bulk shipped in cartons made from sulfite stock. In other words these cartons were not manufactured from acid-free stock. In time, the tin plating started to "micro-flake", and these connectors became erratic.

We recommend the use of Stabilants on these connectors. As it is available as the concentrate (Stabilant 22) or in a partially filled bottle (Stabilant 22S - for Short fill) - where the diluant is added to the concentrate and mixed on site, there are less problems when it has to be shipped by air and the diluant added in the field.

Removal and cleaning of back plane boards
Disassembly can be somewhat tricky because of the potential for damage of components by static electricity.

Obviously any hard drives will have to be removed from the plug-in SCA carriers. It is advisable to make a note of the name (part # or serial #) for each hard drives or SCA's as they are disassembled. What might seem obvious at the time may not be so easy to remember later, especially when several faults occur when time is critical. While this may seen pedantic the use of any Quality Assurance Program (such as one of the ISO's) requires methodology

This caution also applies to any wiring harness connectors in the system. Wires can be tagged using surgical tape until such time as a listing can be made. A rough sketch of each connector location can often save hours of work later on.

Cooling fans
Most caddies that are used with large storage capacity have hard disk drives are fan cooled. If the power supply is deficient in it's voltage output and/or regulation, the needed cooling fans won't work. This can lead to premature failure of the hard disk. The problem might be related to the switching-mode power supply. These contain aluminum electrolytic capacitors. As the efficiency and regulation of the supply can be dependent on the operating frequency, if the capacitor develops resistance, it will both lower the Q of the circuit but also cause a build up of heat. This, in turn, can cause the supply to fail and so on!

Where fan-cooled SCA's are employed, regulation is generally less of a concern. The investment is so large that the type of regulation problems encountered in less expensive ($3,500 and lower) computing systems should not be a problem.

Other types of equipment
The Stabilants can also be used on connectors, the switches in mixers, and in computing equipment. It can even be used in the consolidation of cables. This applies to connectors in general, irrespective of whether they are microphone connectors, patch bays, screw terminals, tab connectors or other types.
What is Stabilant 22?
Stabilant 22 is an initially non-conductive block polymer which when used in a thin film between metal contacts becomes conductive under the effect of an electrical field. This occurs at an electric field gradient such that the material will remain non-conductive between adjacent contacts in a multiple pin environment. In addition, Stabilant 22 exhibits surfactant action, as well as lubrication ability providing a single component resident solution to virtually all contact problems.

When applied to electromechanical contacts, Stabilant 22 can provide the connection reliability of a soldered joint without bonding the contact surfaces.

Where can Stabilant 22 be used?
Stabilant 22 can be used in all types of connectors, at frequencies from to DC to several gigahertz, on fader's or potentiometer's, or in non-inductive (non-arcing) power-interrupt switches. The number of uses are almost limitless.
Is Stabilant 22 just another contact cleaner?
No, Stabilant 22 is a resident potentially electrically active material which through a synergistic combination of effects enhances conductivity within a contact without causing leakage between adjacent contacts. Thus large quantities of the material do not have to be "hosed" on, as is the case with cleaners.
Is Stabilant 22 cost effective?
As Stabilant 22 can be quickly applied to all contacts and connectors in a system, the often difficult diagnostic determination as to which one of many contacts are erratic, can often be eliminated. This can significantly reduce service time in the field and in many cases eliminates the need to return boards for shop service or re-manufacturing. As any service manager knows, the diagnosis of electronic problems, especially where intermittent failures are concerned, is often much more difficult than the actual part replacement; as well as requiring service personnel of exceptional calibre. In many cases the use of Stabilants can thus increase the efficiency of existing staff as well as allowing many connector harness related problems to be handled at a much lower cost.
Many of our users have reported savings of from $250 to $3000 as a result of using $3 to $5 of the material. In many electronic applications demodulation (detection) of RF signals in connectors exhibiting thin film rectification effects can either reduce the signal-to-noise ratio or introduce artefacts which can disrupt data flow. Stabilants can cure these problems.
While Stabilants have demonstrated that they can cut the cost of both shop and field maintenance; their use in the manufacturing of electronic systems can speed up production as well as reducing rejections.
How can Stabilants correct electrical contact problems?
In many electronic applications demodulation (detection) of RF signals in connectors exhibiting thin-film rectification effects can either reduce the signal-to-noise ratio or introduce artifacts which can disrupt data flow. Stabilants can cure these.

While Stabilants have demonstrated that they can cut the cost of both shop and field maintenance; their use in the manufacturing of electronic systems can speed up production as well as reducing rejections.

How does Stabilant 22 work?
Contact failure is rarely caused by a single factor. Thus, treatments that solve only one problem don't necessarily offer a reliable long term solution. For example, cleaners do not prevent the re-entry of contaminants or the reformation of contaminant films; nor do they offer any lubrication. They must be used each time a connector gets dirty. Lubricants in themselves are rarely cleaners. Corrosion inhibitors are neither cleaners nor lubricants and are often specific to one type of metal or plating. Unsaturated oils used as contact treatments can cross-link under the influence of elastomer or thermoset plastic curing agents and accelerants.
While resident in the connector, Stabilant 22 performs several concurrent functions. Its very presence in the contact gap will prevent the entry of outside contaminants. It has sufficient surfactant action to lift surface contaminants and hold them in suspension. In cases where corrosion products are present, Stabilant 22 will penetrate them and prevent rectification effects. Due to its high dielectric constant it will act to form a capacitive layer which is in parallel with whatever residual resistance exists in the contact increasing the passage of AC signals. Given sufficient DC bias within the gaps of the contact the thin film of Stabilant will "switch", conducting by quantum tunnelling, and thus limit the resistance of the contact to a serviceable level.
In what forms is Stabilant available?
The Stabilants are available in several forms. As a concentrate (Stabilant 22), an isopropyl alcohol-diluted form (Stabilant 22A), and an ethyl alcohol diluted form (Stabilant 22E). For example, a given size container of Stabilant 22A will cost about one-fifth the amount of a container of Stabilant 22 as it contains only one-fifth the amount of the concentrate. Another form of packaging is available. Stabilant 22S packages the concentrate such that it occupies one-fifth the volume of an otherwise empty container. This allows the end-user to add his own diluent, and thus saves the added costs of shipping the diluent (e.g.: isopropyl alcohol), as well as allowing the end-user to use an alternate diluent such as one of the Freon-based solvents.
In addition a 0.5 ml vial of Stabilant 22A is available for manufacturers to include with plug-in circuit boards
What is the difference in use of these materials?
Stabilant 22 is most useful where the connections are out in the open - such as card-edge connectors or where the lubricating properties of the material are useful -such as an aid to installing microprocessor IC's or on switches. Where the connections are not too easy to get at or where the user wishes to apply the material to something such as a socketed IC (without removing the IC from its socket), it is easier to use the alcohol diluted form (Stabilant 22A or Stabilant 22E). The alcohol diluent serves ONLY to carry the concentrate into the connector.
What is the best way to apply Stabilant to a contact?
The 15 ml (and the 50 ml) container have "controlled-dropper" type caps that allows Stabilant 22A to be applied directly to such components as socketed IC's, switches, connectors, etc. Some end users prefer to use industrial syrettes to apply the material. Camel's hair brushes can be used to brush it on card-edge connectors or they could be dipped into the dilute material. Most metering type liquid dispensing systems can be used as well.
What packaging is available?
Many manufacturers make large volume purchases, diluting the material for specific applicators used on their production lines. We can supply the concentrate (Stabilant 22), in 0.5 mL, 15 ml, 5O mL, lOO mL, 25O mL, 5OO mL and 1 litre bottles. The dilute (Stabilant 22A or Stabilant 22E, the latter which is available in a limited number of bottle sizes except on special order), are available in 5O mL, lOO mL, 25O mL and 5OO mL containers. We do not have a 1 litre container of the dilute as 500 mL is the largest size bottle that can be shipped by air (in single or multiple packages) without additional restrictions. We maintain our stock in depth and ship most orders the next day that they are received. ( On large quantities , more time may be required) For companies which want to use the material as a stock store item, we can produce custom labels with your part or stock number. The 15 mL sizes are in dropper bottles, and these are available on request for the 50 mL sizes as well.
Custom labelling has been provided for many manufacturers who wish to assign their own stock control number, or to distributors who wish to market the product under their own logo. Obviously this requires purchase in of the product in suitable quantities.
Is it available in a spray can?
No. Why waste the material? We would like to think we are environmentally responsible and safety conscious. This ruled out the use of either a chlorofluorocarbon or highly inflammable mixture of butane and propane as a propellant.
In addition even Stabilant 22A for example, has only about 71200th the solvent impact as conventional contact cleaning solvents, over a three year time span. As Stabilant 22 contains no solvent it has absolutely minimal environmental impact and is, therefore, becoming the treatment of choice for many service organizations!
Just how much should be used?
Normally, a final film thickness of from 0.5 to 2 mils of the concentrate is all that it necessary. In other words, you want just enough to fill up the interstices between the contact's faces. When using Stabilant 22A, or Stabilant 22E, use enough so that once the isopropyl alcohol (or ethyl alcohol), evaporates the desired 0.5 to 2 mil film of Stabilant 22 remains.
In applications to moving surfaces, such as in slip-rings or potentiometers, film thickness should be minimized to the point where "hydroplaning" won't occur.
What is the 15 ml service kit?
This was made up at the request of several manufacturers who wanted a standard kit that they could issue to their service personnel. It consists of a 15 ml dropper bottle of Stabilant 22A and some applicators, all in a small capped cardboard tube that can be tossed into a tool box without damage. As noted, we can provide these kits with special labels when large volume orders are involved.
Does the action of Stabilant deteriorate with age?
In some field trial applications lasting over fifteen years Stabilant 22 has shown no sign of reduced effectiveness. With a high molecular weight and a very low vapor pressure, little is lost by evaporation. Unlike some other contact protection oils, Stabilant 22 will not cross-link when exposed to free machining materials such as high sulfur brass, or when used on contacts where agents used to promote cross linking of thermosets or elastomers are present in the environment or in the actual connector components. Unlike non-saturated oils, Stabilant 22 does not "varnish".

Revision 4

Stabilants™ are a product of Dayton Wright research & development and are made in Canada


NATO Supply Code 38948
15 ml of S22A has NATO Part # 5999-21-900-6937


MATERIAL SAFETY DATA SHEETS ARE AVAILABLE ON REQUEST.