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Socket Mounting Recommendations and Reflow Profile E-tec Interconnect Ltd, Industrial Zone C, CH-1072 Forel (Lavaux), Switzerland Phone +41-21-781 08 10 · www.e-tec.com · info@e-tec.com E-tec Socket Mounting Recommendations PRELIMINARY 4 Verifying the Assembly After the socket has been reflowed to the PCB, open and short testing should be partaken to ensure proper assembly. The assembly house typically performs x-ray inspection to verify non- shorting of pins. However, as this is only a visual inspection, we recommend using a continuity tester or ohmmeter and simply sweeping random rows and columns of pins to ensure no shorting of pins. No damage to the springs will occur if very slight pressure from the meter’s tips is applied (just touch the probes to the springs). For fine pitch sockets, a microscope would be helpful in placing the meter’s tips appropriately. After verifying the absence of shorts, open testing should be performed. The most direct, yet tedious, method is to use the continuity tester to directly probe each pin to a breakout or test point on the board. Again no damage will occur if the probes are touched to the springs. If heavy pressure is required to push the socket body towards the PCB to achieve continuity, this means a poor solder joint. If no such test points exist, then the BGA’s via field on the backside of the PCB should be kept solder-mask free to allow for such probing. If the via field is kept open, a simpler open testing method can be performed. Simply use a wet sponge (or some other conductive material) and hold it onto the via field. This shorts all the pins together on the PCB. Insert one probe of the continuity tester into the sponge. Now sweep the pins of the socket with the other probe and check for continuity. If the above procedures show any shorts or opens, then it is advisable to have the assembly house re-evaluate the assembly method used. An incorrect stencil can lead to too much or too little solder paste, easily leading short or open conditions and a solder paste with Ag contents (>=0.5%) may also result in solder joint failures. These are the primary reasons for socket mounting failures. Important Notes: a) Screw/Twist Lock Socket When tightening the lid of a Screw or Twist Lock socket, it is imperative to not over-tighten the retention screws, otherwise irreparable damage may occur. Such damage is not covered by warranty and will be solely the end user’s responsibility. The maximum allowed torque on these retention screws is 7cN-m (10oz-in) for sockets up to 800 pins and for sockets as of 800 pins the torque value needs to be increased but should not exceed a maximum of 10cN-m (14oz-in). E-tec sells the torque screwdriver TOL-7CN-TORQUE which is preset to 7cN-m, but which can be adjusted to higher torque values for the high pin count sockets. |
