What are the preventative maintenance and cleaning methods recommended for various socket types?

Summary

Over the lifetime of a socket, various factors can cause the socket performance to degrade. The purpose of this document is to detail preventative maintenance and cleaning methods recommended for various socket types. BPM Tech Support should be contacted if within the normal life cycle of a socket, following these procedures does not improve socket yield or if socket yields deteriorate rapidly early in the life of a socket.

Details

Socket Categorization  There are 3 basic types of sockets from a cleaning perspective. Elastomer-based sockets. Elastomer sockets have a springy socket membrane at the base of the socket which forms a group of pads as opposed to individual pins. These are always compression mount sockets i.e. that they are mounted onto the PCB using screws or bolts. Pogo pin-based sockets. As the name suggests Pogo pin-based sockets use a pogo pin as the electrical contact (http://en.wikipedia.org/wiki/Pogo_pin). Pogo pin-based sockets are always compression mount sockets also. Standard Sockets. All other sockets are classified as standard sockets.

Prevention Techniques

Perform regular visual inspections to identify signs of abnormal wear Check specifically for discolored, bent, or broken pins, and non-uniform locations within the socket housing. If any concerns arise then compare the socket to another socket of the same type (if available) to see if they both have the same characteristics. Differences may point to an area of concern. Actuate/open the socket and check if all parts seem to be moving properly. Make sure there is no unusual friction or noise of parts grinding against each other. Ensure proper mounting of the socket to board interface (i.e. load board). Determine and minimize outside sources of dust and debris. One method that is helpful here is to examine the composition of any foreign matter that is found in the sockets. This can be a good clue as to where issues are coming from. Also, see the Socket Degradation analysis section below for additional information. Keep the relative humidity levels as low as possible in the programming facility. When relative humidity levels are high it is easier for contamination to stick to sockets and may be harder for them to be properly cleaned. Never use bare fingers to reach in or touch any pins or parts inside of the socket nest. Oil and dermis will contaminate the contacts and cause premature failure. Do not use unapproved cleaning techniques which could cause damage to any part of the socket. Some cleaners do not work well with plastics that could make up the shell of a socket and others can damage parts of the connecting pins. Be extra careful when setting up new jobs. Collisions between parts and sockets don’t just damage parts, but can also be harmful to sockets. Do not modify, refinish or re-surface any part of the socket.

Causes for Socket Degradation and sequence of steps for resolution
There are 3 primary causes of degraded socket performance.

As sockets are used, solder is transferred from the IC devices to the socket contacts. This solder oxidizes and degrades the electrical signal needed to complete the programming operation. Compressed air and Nanotek brush used in combination Cleaning Devices Chemical Cleaning The signal can be further degraded as organic and inorganic debris collects on the contact surfaces. This debris comes from the programming environment as well as from the actual devices being programmed. Compressed air and soft bristle brush used in combination Cleaning Devices Chemical Cleaning Mechanical damage to the contact interface. Each time a device is inserted into a socket, a small amount of mechanical wear can occur. This can damage the critical gold plating which is needed to maintain an electrical interconnect. If the socket is inexpensive then it should be replaced. If the socket is a pogo pin style socket then possibly the pins themselves can be replaced and replacement parts on the socket refurbished. Contact BPM Tech Support. Sockets can also be sent to an outside company like Nu Signal. They specialize in cleaning and resurfacing socket pins.

Procedures applicable to specific socket categories

Elastomer Sockets   Compressed air. This should be the standard preventative maintenance procedure for this socket type. Use of 3M Magic Tape (3M model number: 3M-MP-18) followed by the compressed air routine. When yield has become insufficient, contact BPM for a replacement socket. Pogo Pin sockets All Cleaning methods except 3M Magic Tape and Chemical Bath Cleaning are open for this type of socket. Chemical Bath Cleaning is not recommended since chemicals can get inside the housing of a Pogo Pin during the cleaning process but are not easily removed. Once inside the Pin, they will cause the pins to work improperly. When yield has become insufficient, contact BPM for replacement socket, or contact Nu Signal for special cleaning options Pogo pins have the added advantage of being replaceable. Please contact BPM to determine the cost and logistics of replacing pins. Standard Type Sockets. All cleaning Methods except 3M Magic Tape are open for Standard Type sockets. When yield has become insufficient, contact BPM for replacement options. Compression Mount Sockets All Elastomer, All Pogo Pin, and some Standard sockets will fall into this category. There is a second connection interface which is between the socket and the PCB. Whenever sockets are mounted to the board it is important to ensure the board is clean and free of contaminants (lubricants, flux, particles). One method is to wipe the socket pads on the board using a soft cotton cleaning tip (or sponge-tip). Soak the tip in alcohol or contact cleaner and use gentle pressure. This step should be followed with compressed air to remove any fibers from the pads. When mounting sockets to the PCB torque specifications must be followed. Contact BPM Tech Support. If incorrect torque is applied to the socket, it may result in poor yields.

Socket Cleaning Procedures

Compressed air. Using a clean dry air source blow compressed air into the socket nest. If possible vary the angle and position of the nozzle tip so that any dust/debris which is inside the socket nest is pushed on from different angles and therefore has the best opportunity to be pushed out of the frame. The distance from the tip to the socket is dependent on the amount of airflow through the nozzle but in general, the tip should be kept more than 2.54cm (1 inch) away from the socket during this process. Line pressure should not exceed 30 psi. This cleaning technique should be the most regularly applied technique and should be used as a follow-up technique after any of the other cleaning techniques have been implemented. Soft Bristle Brush Cleaning Soft Bristle Brush Cleaning is generally used for helping to remove any dust and debris from inside the socket nest. To do this, gently brush the socket nest from multiple angles to help dislodge any dust or debris. 3M Magic Tape (3M model number: 3M-MP-18) This can be used to remove any dust or dirt that has accumulated on the pad of an elastomer socket. To do this place the magic tape onto the pad and then simply remove it. The idea is that any dust or dirt will remain attached to the tape which can then be discarded. The tape should not be allowed to sit on the surface and should not be pressed into place with a lot of force. Please note, applying too much pressure onto the Elastomer pad can cause damage. This method should be used only after a concern has been identified. Nanotek Brush Cleaning Nanotek Brush Cleaning is generally used for helping to remove contamination/build-up on a contact pin that is due to solder migration. To do this, gently brush the socket pins in the socket. Since the brush type is metal, extra care needs to be taken to ensure that damage to the device pins does not occur. The force required for gently cleaning a socket pin is roughly equivalent to the same force used when brushing your teeth. Additional force is not guaranteed to give better cleaning results and as stated earlier could potentially damage device pins. The Nanotek brush should only be pulled (never pushed) when cleaning. If the brush is pushed then bristles can deform which will reduce the life of the brush. When looking at a brush from the side you will notice a slight angle to the bristles, please be sure to take advantage of this angle when reaching into tight spots so that a direct vertical pushing of the brush into the socket can be avoided. The Nanotek brush should be mainly used to brush the specific points where the socket makes contact with a device. Other than general cleanliness, cleaning other locations will not affect the contact interface between the socket and device. Once the contact points are determined, brush 10 to 20 times for each point to ensure a thorough cleaning. In most cases, in order to reach all of the contact points the socket will need to be actuated in the same manner as would be done when manually placing a device into it. Different size Nanotek brushes are available for use in different applications. In general, the below table should be used to determine the best size brush for cleaning different socket types. Size of Device Programmed by the Socket Size of Nanotek Brush to use for Cleaning < 5 mm x 5 mm 1 mm < 10 mm x 10 mm 2 mm > 1 0mm x 10 mm 3 mm Different Bristle-type Nanotek brushes are available for use in different applications. In general, it is recommended that 0.03mm O.D. bristles are used when preventative maintenance is being done and 0.05mm O.D. bristles are used when cleaning sockets for which reduced functionality has already been observed. Here is a full table of brushes available from BPM Microsystems. These brushes can also be purchased directly from Kita Manufacturing. BPM Part # Size of Nanotek Brush OD of Nanotek Brush Bristles CNBRUSH-1-003 1 mm 0.03 mm CNBRUSH-1-005 1 mm 0.05 mm CNBRUSH-2-003 2 mm 0.03 mm CNBRUSH-2-005 2 mm 0.05 mm CNBRUSH-3-003 3 mm 0.03 mm CNBRUSH-3-005 3 mm 0.05 mm   Cleaning Devices Cleaning devices can be purchased that are made based on the size and shape of the device being programmed by the socket in question. To use these cleaning devices Actuate the socket in the same manner as would be done to manually place a device into it. Place a Cleaning Device into the socket instead of the standard device. Actuate, remove, and again place the Cleaning Device into the socket for a total of 3 insertions when preventative maintenance is being done or 6 insertions after functionality concerns have already been identified. Finally, remove the Cleaning Device from the socket. Cleaning devices are rated to clean sockets for 250 touchdowns after which they should be discarded and a different cleaning device used. Cleaning devices are best used as tools for preventative maintenance. Chemical Tip Cleaning. Using a medium to firm non-metal bristle brush and a commercially available cleaning solution clean the contact points of the Device Socket. To do this, wet the brush with the cleaning solution and brush in one direction for several brush strokes. Change the direction several times and use several brush strokes in each direction. Cleaning should be done while the socket is both in the actuated and non-actuated socket positions as different positions will lend themselves to better access depending on the specific socket being cleaned. (See pictures below). – Do not twist the brush in a circular pattern. – Never push on the socket brush during the cleaning process. This greatly lessens the chances of the brush or the socket itself being damaged during cleaning. – Do not apply excessive force when using the brush. The chemical being applied is expected to do most of the work in cleaning so large amounts of force should not be required. – Do not apply excessive amounts of cleaning solution to the brush. Please remember that only the contact points need to be cleaned. This warning is especially important for Pogo Pin based sockets for which the cleaning solution should not be allowed to make its way into the pogo pin housing. Approved solutions for bristle brush cleaning are: – Envi-Ro-Tech 1676, general-purpose defluxer, manufactured by Tech Spray, Inc., PO. Box 949, Amarillo Texas, 79105 – Isopropyl AlcoholPosition A – contact pins exposed/actuated socket Position B – contact pins retracted/non-actuated socket Ultrasonic Bath Cleaning. This method of cleaning has been available for a long time and can be very effective for cases where the socket can be removed from the PCB. The disadvantages are that in general, a whole socket will need to be subjected to the cleaning process so the choice of cleaning solution is critical. Never immerse the socket in an untried solution. If a newly available solution is applied to the socket this should be done first using the Chemical Tip Cleaning method so that any damage to socket pins or housing can be observed. The standard method for cleaning a socket using an ultrasonic bath is to: The socket should be removed from the PCB. Place the Socket into a small glass container filled with cleaning solution. Place the small glass container into the ultrasonic bath. Run the ultrasonic bath at around 25 deg C to 40 kHz for 60 min (unless otherwise specified by cleaning solution chosen). Remove the socket from the bath and use a compressed air routine to remove as much solution as possible. Bake socket for 30 min at 65 deg C to dry up the cleaning solution. Visually inspect that all cleaning solution has evaporated. If not sure, let the socket sit for an additional 30 min before returning it to the PCB. Outside Cleaning Services Finally, there are companies that specialize in cleaning and revitalizing previously used sockets to maximize the socket life. The disadvantage of this is that sockets will need to be shipped off-site and there is an additional time delay, but the result in time-saving and cost-effectiveness can easily justify this method. One vendor that BPM has used with good success in the past is Nu Signal.