ATLAS Pixel Detector Flex Hybrid Assembly Manual version 1.0 27 September, 2002
1 Introduction 1.1 Purpose This manual describes the equipment, materials and step-by-step procedures to be used in the construction of the ATLAS Pixel Detector Flex Hybrids. 1.2 Scope It assumed that the reader is familiar with the specific instructions for operating the equipment and using the materials described in this manual. Any deviations from normal operation, in addition to any standard settings, are also listed with the procedure to which they apply. 1.3 Logging and Tracking 1.3.1 Log books Log books are provided for each major step of flex hybrid assembly performed at OU and Albany. Even when test data are kept in computer files, the serial number of each flex processed is entered into the log book along with any unique conditions, settings or deviations from the procedures described in this document. This includes errors or mistakes recognized during processing. Each log book shall contain a copy of the relevant procedure description contained herein. 1.3.2 Production Database (PDB) 1.3.2.1 For each flex hybrid processed, there shall be an entry in the flex PDB describing the procedure completed and containing a reference to the log book and page which describes the procedures, settings, etc. used on each flex. These PDB entries shall be made in the way described in the step-by-step instructions that follow. 1.3.2.2 Test and inspection results must also be uploaded to the PDB. This can, in most cases, be a Pass or Fail flag, plus date of test and in which log book (and computer file) the test data is contained. When a data file is generated by the test system, a link to the file location shall also be entered into the database record. (The test tables for the flex hybrid have not yet been implemented, so results and information must be uploaded as comments, for now.)
2 Assembly Steps Activity Section (Flex fabrication) Visual inspection 3 Lamination of flex onto FPCB 4 (Load passive components) Update category type in PDB to FlexLoaded Chemically clean flex 5 Plasma clean flex 6 Wire bond test access 7 Pot above wire bonds 8 Envelope inspection 9 Ship to Albany (1) HV test 10 Ship to OU or Genova Notes: (1) Shipments shall conform to procedures defined in PDB shipping document.
3 Visual Inspection 3.1 Purpose For production, currently limited to measuring the wire bond pad widths on a sample. 3.2 Materials and Equipment 3.2.1 Logbook: VI 3.2.2 14" optical comparator with 50x lens set, surface illumination and digital readout 3.2.3 Bare flex 3.2.4 Vacuum bare flex holder for optical comparator 3.2.5 Delrin standoff blocks 3.3 Step-by-Step Instructions 3.3.1 Secure vacuum bare flex holder to optical comparator bench using built-in delta-slot clamps. Use 2 standoffs between flex holder and stage. 3.3.2 Connect house vacuum to bare flex holder and open valve. 3.3.3 Place bare flex on holder and orient holder with top side of flex facing the comparator (Figure 1). 3.3.4 Measure the width of at least one FE bond pad in each of the four quadrants of the flex. 3.3.5 Record the measurements in the log book, noting the positions of the measurements by FE number (see Figure 3).. 3.3.6 Rotate the flex holder 90o so that the edge of the flex is facing the comparator (Figure 2). 3.3.7 Measure the thickness of the flex circuit in at least two locations. 3.3.8 Record the measurements values in the log book, indicating the positions of the measurements by FE number, left or right (see Figure 3). 3.3.9 Storage location TBD. 3.4 Acceptance Criteria 3.4.1 Bond pads must be at least 80 µm wide. 3.4.2 Compunetics flex thickness should be 4 mils ± 10%. 3.4.3 Dyconex flex thickness is not determined at this time.
Figure 1. Figure 2.
Figure 3.
4 Lamination of Flex onto FPCB 4.1 Purpose The Frame PCB (FPCB) serves many purposes, including provision of connections for flex hybrid and module test, protection of the bottom solder mask /cover layer and easy handling during flex hybrid and module assembly. Because the FPCB is used in registration of the flex hybrid to the module, the flex must be attached accurately (± 300 µm). The custom laminator provides accurate alignment and an adhesive application and curing system. 4.2 Materials and Equipment 4.2.1 No log book is required for this process. 4.2.2 Laminator 4.2.3 Loctite Chipbonder 2614 in caulking gun 4.2.4 Bare Flex 4.2.5 FPCB 4.2.6 Acetone 4.2.7 Paper towels 4.2.8 Nylon gloves 4.2.9 Antistatic zip lock bags 4.2.10 Bar code labels 4.2.11 Computer access to the PDB 4.2.12 Bar code scanner 4.3 Safety Precautions 4.3.1 The laminator has components which get hot enough to cause severe burns. Observe where these areas are and avoid contact with them. 4.3.2 See the material safety sheets for Loctite Chipbonder 3416, on file in the lab. 4.3.3 Acetone is toxic. See the material safety sheet, on file in the lab. 4.4 Step-by-Step Instructions 4.4.1 Connect laminator to house vacuum, if not already connected. Check the vacuum gauge adjacent to the house vacuum service tap for at least 20 mm Hg. If less, check for vacuum leaks or other equipment in use that may be too leaky. 4.4.2 Turn laminator power on. 4.4.3 Set Watlow temperature controller on the laminator control panel to 315 o F and allow unit to reach this temperature before proceeding. 4.4.4 Turn on the vacuum switch on the laminator control panel. 4.4.5 While wearing nylon gloves, place 5 Compunetics or 3 Dyconex flex on the flex holders, starting from the side where the vacuum enters the flex work holder. Also, the bias hole in the flex is placed toward the FPCB's on the flex work holder. Be sure to mount the flex so that the alignment pins on the flex holders pass through the alignment holes on the flex.
4.4.6 Record the measurements in the log book, noting the positions of the measurements by FE number Place 5 FPCB's (even if there are only 3 flex) on the FPCB positions of the laminator, taking care that all three alignment pins mate completely with the corresponding holes in the FPCB's. 4.4.7 Flip the silk screen over the FPCB's and apply a 1 to 2 inch bead of Loctite Chipbonder 3614 adhesive to one end of the silk screen. 4.4.8 Using the supplied squeegee, apply an even layer of adhesive to the FPCB's through the silk screen. 4.4.9 Return the silk screen to the rest position. 4.4.10 Flip the flex holder bar over the FPCB's and lock into place. 4.4.11 Press down on the pressure bar until it locks into place. 4.4.12 Wait one minute. 4.4.13 Turn off the vacuum switch on the laminator control panel. 4.4.14 Release the laminator pressure bar. 4.4.15 Flip the flex holder bar back into the loading position. 4.4.16 Remove laminated assemblies. 4.4.17 Inspect the laminated assemblies. 4.4.18 Attach bar code label and write s/n on flex as described in module serial numbering document. 4.4.19 Place each FPCB in a zip lock bag. 4.4.20 When finished, carefully scrape the remaining adhesive from the silk screen using the squeegee. Next, clean the remaining adhesive from the silk screen and other parts of the laminator using acetone and paper towels. 4.4.21 Enter each flex serial number as category type "FlexOnFrame" into the PDB using the bar code scanner and the web interface to the PDB. 4.4.22 Storage location TBD. 4.5 Acceptance Criteria 4.5.1 Alignment hole in flex shall be aligned to hole in FPCB, as determined by unaided visual inspection. 4.5.2 The flex tails shall be completely adhered to the FPCB and there should be adhesive under all bond pads. 4.5.3 There shall be no adhesive on bonding pads or flex. 4.5.4 The flex shall be flat on the FPCB, as determined by using a gloved finger to apply gentle pressure to the surface of the flex starting at one tail and sliding the finger to the other end. The flex shall remain flat against the FPCB during and at the end of this operation.
5 Chemical Cleaning 5.1 Purpose As received from the loading vendor, the flex circuit adheres to the FPCB. This is caused by trapping of solder resin and other contaminants between the flex and the FPCB during automated cleaning at the assembly vendor. The chemical cleaning process removes contaminants from the flex and FPCB. 5.2 Materials and Equipment 5.2.1 Log book: CC 5.2.2 Loaded flex on FPCB 5.2.3 Latex gloves 5.2.4 Safety goggles 5.2.5 Ultrasonic cleaner 5.2.6 Citrasafe 5.2.7 Flex holder for cleaning 5.2.8 DI water 5.2.9 Micro tips / Plastic sticks 5.2.10 Propanol 5.2.11 Measuring cup 5.2.12 Container for rinsing boards 5.2.13 Utility sprayer 5.2.14 Environmental chamber 5.2.15 Zip lock bags 5.2.16 Computer access to the PDB 5.2.17 Bar code scanner 5.3 Safety Precautions 5.3.1 Use gloves to protect hands from Citrasafe and propanol; both can severely dry skin. Use moisturizing hand soap on skin that comes into contact with either. 5.3.2 Use safety goggles while handling Citrasafe and propanol or propanol + water mix. Flush eyes immediately with running water if exposed. Contact supervisor as soon as possible or seek medical attention. 5.3.3 See material safety sheet for Citrasafe. 5.3.4 See material safety sheet for propanol. 5.4 Step-by-Step Instructions 5.4.1 Open the window adjacent to the ultrasonic cleaner. 5.4.2 Clean the Ultrasonic cleaner, micro tips, glass tray, plastic box and the jig (with dish washing detergent, if needed). Rinse with DI water. 5.4.3 Wash your hands and wear latex gloves. 5.4.4 Place the flex in the jig slots. Insert the micro tips between the flex and the FPCB so that the flex is held away from the FPCB. 5.4.5 Fill the ultrasonic cleaner with Citrasafe to the fill line in the tank. Use fresh Citrasafe if the use limit of the used Citrasafe has been reached (TBD.).
5.4.6 Place enough DI water and propanol in a 1:1 ratio (using the measuring cup) to cover the FPCB's mounted in the jig. 5.4.7 Fill the utility sprayer to the fill line with DI water. Pump up the sprayer to operating pressure. 5.4.8 Place the jig holding the flex circuits in the ultrasonic cleaner. Switch on the ultrasonic cleaner and set the timer for 10 minutes. After 10 min., remove the flex from the ultrasonic cleaner. 5.4.9 Place the jig in the rinse container and rinse the flex thoroughly in the water + propanol mixture, using manual agitation. Replace the mixture after the prescribed number of uses (TBD). 5.4.10 Place the jig in the laboratory sink and spray with DI water from the utility sprayer until the water runs clear. Take care to rinse between the flex and the FPCB thoroughly. 5.4.11 Remove the flex from the jig and place them on a shelf in the environmental chamber. 5.4.12 When finished processing a batch or when the environmental chamber is fully loaded, heat chamber to 75 deg. C until flex are dry. Flex will likely dry in different time intervals, so monitoring of drying process is required. 5.4.13 Place each flex in a zip lock bag when dry. 5.4.14 Storage location TBD. 5.4.15 Upload a comment, using the bar code scanner to enter the flex serial numbers for each flex for which the following information is the same (using the batch upload Java applet): 5.4.15.1 "Chemically cleaned" 5.4.15.2 Date 5.4.15.3 Technician name 5.4.15.4 "Logbook CC" + page number 5.5 Cleanup 5.5.1 Drain the Citrasafe from the ultrasonic cleaner and store it in the used Citrasafe container. 5.5.2 Dry the inside of the ultrasonic cleaner tank with a clean paper towel. Cover the ultrasonic cleaner with its lid. 5.5.3 Clean the rinse container with dish washing detergent and perform the final rinse with DI water. Place it upside down to drip dry. 5.5.4 Log deviations from this procedure and other observations along with the flex serial numbers in the CC log book. 5.5.5 Update the PDB comments using the Java application. 5.6 Acceptance Criteria 5.6.1 Flex shall not adhere to the FPCB except where attached with adhesive, as described in section 4. 5.6.2 Flex and FPCB shall be free of loose debris and contamination. 5.6.3 Flex and FPCB shall be free of water spots and other discoloration.
6 O 2 Plasma Cleaning 6.1 Purpose Plasma cleaning prepares the flex bond pads for wire bonding and improves wire bond pull strength. 6.2 Materials and Equipment 6.2.1 Log book: PC 6.2.2 Loaded and chemically cleaned flex on FPCB. 6.2.3 Plasma cleaner with O 2 and N 2 gas supply cylinders 6.3 Safety Precautions 6.3.1 The plasma cleaner emits UV radiation during the cleaning process. Be sure to close the outer steel door to block this radiation. 6.3.2 Oxygen accelerates combustion. Be sure to close the O 2 cylinder valve when cleaning operations are complete. 6.3.3 Check that the exhaust vent fan is on before beginning operation. The switch is in the machine shop. 6.3.4 Check the oil level in the vacuum pump before turning it on. 6.4 Step-by-Step Process 6.4.1 Open the O 2 and N 2 cylinder valves. 6.4.2 Turn on the vacuum pump. 6.4.3 Turn on the exhaust fan and verify its operation. 6.4.4 Place two chemically cleaned flex on FPCB on each of the three shelves in the plasma cleaner. 6.4.5 Close the doors and start Program 1. 6.4.6 When the program is complete, press the Stop button. The flex are now ready for wire bonding. Handle the FPCB by its edges and be careful not to touch the metal on the flex or the FPCB. 6.4.7 Don't process another batch until the current batch is used up. Any flex not wire bonded within 24 hr. should be cleaned again using Program 2, just prior to wire bonding. 6.4.8 Store plasma cleaned flex in the plasma cleaner oven until it is wire bonded. 6.4.9 Upload a comment, using the bar code scanner to enter the flex serial numbers for each flex for which the following information is the same (using the batch upload Java applet): 6.4.9.1 "Plasma cleaned" 6.4.9.2 Date 6.4.9.3 Technician name 6.4.9.4 "Logbook PC" + page number 6.5 Acceptance Criteria 6.5.1 Flex and FPCB metal should be free of visible contaminants.
3.1.1 Put a small drop of DI water on an exposed trace on the flex. If it spreads, then it has passed the test. Shake the water off and allow the flex to air dry in the clean room.
7 Au Ball Wire Bonding 7.1 Purpose To wire bond the test gap and to wire bond the test pads to the FPCB. 7.2 Safety Precautions The bonding capillary heater is very hot - avoid contact. 7.3 Materials and Equipment 7.3.1 Log book: WB 7.3.2 Loaded, chemically cleaned and plasma cleaned flex on FPCB 7.3.3 Westbond 2000 series bonder configured for Au ball bonding 7.3.4 Au ball bonding capillary (specific tools still under evaluation) 7.3.5 1 mil Au bonding wire: 7.3.5.1 99.99% Au + 0.01% Be 7.3.5.2 3% - 5% elongation, 7.3.5.3 On 2" dual flange spool 7.3.6 Wire bonder work holder for FPCB 7.3.7 Computer access to the PDB 7.3.8 Bar code scanner 7.4 Step-by-Step Instructions (Still under development) 7.4.1 Open house compressed air valve on back of bonder. Pressure must be 80 PSI ± 20%. 7.4.2 Open house vacuum. Vacuum pressure must be at least 20 mm Hg. 7.4.3 Turn on bonder. 7.4.4 Turn on despooler. 7.4.5 Turn on external light source. 7.4.6 Wait for machine initialization to complete. 7.4.7 Open the Au ball bonding program for the test bonds (check WB log book for current program in use). 7.4.8 Verify that the machine is configured for 2700B operation. 7.4.9 Verify that the tool overdrive is 5 mil. 7.4.10 Verify that tool heat dial is set at 3.5 (or current setting suggested in WB log book). 7.4.11 Place FPCB securely on work holder. 7.4.12 Pinch red vacuum hose leading to stage once or twice while observing flex circuit. It should visibly be pulled all the way down to the FPCB surface when the hose is released. If not, reposition the FPCB on the work holder and try again. 7.4.13 Check bond settings on the bonder against latest recommendations in WB log book. 7.4.14 Start bonding in Pause mode to verify that bonder is working properly. Once satisfied that settings are OK, put bonder in Automatic mode. Observe bonder while in action. Pull failed wires and rebond them.
7.4.15 When bonding is complete, check for shorted or missing wires. (During development, record missing, broken and shorted bonds in the log book.) 7.4.16 Place FPCB in shipper and secure Plexiglas cover with the four thumb screws. 7.4.17 Be sure to reverse the procedures of steps 7.4.1-7.4.5 when through bonding for the day. 7.4.18 Storage location TBD. 7.4.19 Upload a comment, using the bar code scanner to enter the flex serial numbers for each flex for which the following information is the same (using the batch upload Java applet): 7.4.19.1 "Test interface wire bonded" 7.4.19.2 Date 7.4.19.3 Technician name 7.4.19.4 "Logbook WB" + page number 7.5 Acceptance Criteria 7.5.1 There shall be no shorted nor missing wire bonds. 7.5.2 All second bonds shall have a security bond centered on the wedge.
8 Wire Bond Potting 8.1 Purpose The wire bonds made in step 7 must be potted to prevent damage from handling during the remaining test and assembly steps, including module assembly and testing. The encapsulant bead is removed with tweezers before the final flex cut is made at each end, taking the wire bonds with it. 8.2 Materials and Equipment 8.2.1 Log book: PA 8.2.2 EFD fluid dispensing system 8.2.3 10 cc syringe with piston 8.2.4 1/2" x 20 ga. metal dispensing tip 8.2.5 Dow Corning Sylgard 186 potting compound 8.2.6 Weight scale 8.2.7 Disposable mixing tins 8.2.8 Disposable wooden mixing stick 8.3 Safety Precautions 8.3.1 Place used tips in an empty plastic bottle. Do not throw tips directly into the trash, as this presents a hazard to the custodial staff. 8.3.2 See material safety sheet for Sylgard 8.4 Step-by-Step instructions (Manual method - automated method under development.) 8.4.1 Weigh out Sylgard resin and hardener in 10:1 ratio in a mixing tin. 8.4.2 Mix Sylgard thoroughly with wooden stick. 8.4.3 Pour Sylgard into syringe 8.4.4 Place piston in syringe and connect to dispenser air tube. Store syringe in syringe holder when not applying Sylgard. 8.4.5 Set EFD dispenser in continuous flow mode. 8.4.6 Lay a few practice beads on a piece of paper to get a feel for the consistency and flow of the Sylgard. 8.4.7 Use multiple passes to completely cover the wire bonds. Avoid covering the active flex area beyond the bond pads. 8.4.8 If the process does not meet the acceptance criteria, cure the encapsulant, then remove it with tweezers and wire bond again. 8.4.9 For rapid curing of the Sylgard, place the FPCB's into the environmental chamber and bake for 30 min. at 100 o C. For room temperature cure, place in N 2 cabinet in the clean room for 48 hours. 8.4.10 Place FPCB in flex shipper when curing is complete and secure cover with the four thumb nuts. 8.4.11 Storage location TBD. 8.4.12 Upload a comment, using the bar code scanner to enter the flex serial numbers for each flex for which the following information is the same (using the batch upload Java applet):
8.4.12.1 "Test interface wire bonds potted" 8.4.12.2 Date 8.4.12.3 Technician name 8.4.12.4 "Logbook PA" + page number 8.5 Acceptance Criteria 8.5.1 The encapsulant shall be completely cured with no tackiness. 8.5.2 There shall be no shorted or broken wire bonds visible under magnification. 8.5.3 The wire bonds shall be completely covered by the encapsulant. 8.5.4 The encapsulant shall not contact any components on the flex circuit. 8.5.5 The encapsulant shall not contact any FE bond pads.
9 Envelope Inspection 9.1 Purpose Based on early estimates of the thickness of the sensor, FE's, flex hybrid, adhesive layers and components plus the estimated tolerances, an envelope within which the flex hybrid and components must fit was defined. As we approach production, many of these thicknesses are known to be thinner than originally estimated. As a result, the only inspection that may be necessary is to check that none of the components are misplaced or tombstoned. This is also done at the assembly vendor, so only a sample may need to be checked. However, a procedure has been developed based on the originally tightly constrained envelope definition. This is the procedure which follows and it may be easily adapted in production for less thorough inspections. This procedure does not yet include inspection of the MCC placement and wire bonding, as this procedure is not yet being performed at OU. 9.2 Material and Equipment 9.2.1 Log book: EI 9.2.2 Loaded flex on FPCB 9.2.3 14" optical comparator with profile lighting and 10x lens set 9.2.4 6" vacuum chuck 9.2.5 6" vacuum FPCB work holder 9.2.6 Map of component locations and names 9.2.7 Nylon gloves 9.2.8 Computer access to the PDB 9.3 Safety Precautions 9.3.1 Use nylon gloves when handling flex+fpcb 9.3.2 Be very careful not to strike or scratch the optical comparator lense when orienting the FPCB. 9.4 Step-by-Step Procedure 9.4.1 Turn "ON" both profile lamp switches on the optical comparator. Connect the 6" vacuum holder to the house vacuum and turn the vacuum valve on. 9.4.2 Place the vacuum work holder on the vacuum chuck. 9.4.3 Place a flex on the vacuum work holder. The vacuum can be temparaly released by pinching or crimping the vacuum hose to facilitate positioning the work holder. 9.4.4 Place the flex facing the lens as shown in Figure 1.
Figure 4. Figure 5.
Figure 6 9.4.5.Zero the scale of the optical comparator to the top surface of the flex. 9.4.6 Increase the height of the work bench by 0.625 mm and check for the tolerance of the capacitors. The capacitors checked are C23, C24, C25, C26, C27, C28 andc29 (Figures 2 & 3). Figure 7 9.4.7 Adjust the focus knob to view components R6, R9, R5, R10, R11, R12, R13 and C22 (Fig. 4). 9.4.8 Adjust the bench to the right so that the remaining LDC's (Local Decoupling Capacitors - those that are in line with the FE bond pads on the flex) are visible (Fig. 5).
Figure 8.
Figure 9 9.4.9 See Figure 6.
Figure 10. 9.4.10 See Figure 7 9.4.11 See Figure 8. Figure 11.
9.4.12 See Figure 9. Figure 12. 9.4.13 See Figure 10.
Figure 13., 9.4.14 See Figure 11.
Figure 14. 9.4.15 See Figure 12. Figure 15..
9.4.16 See Figure 13. Figure 16. 9.4.17 See Figure 14. Figure 17. 9.4.18 See Figure 15
Figure 18. 9.4.19 See Figure 16 Figure 19.. 9.4.20 Record acceptance criteria violations in log book and mark flex as "Failed EI" with label on FPCB (details TBD). 9.4.21 Upload test data and result (undefined).
9.5.Acceptance Criteria 9.5.1 The acceptance criteria are given in the step-by-step instructions. 9.5.2 In addition, no tombstoned or broken components can be accepted.