Masking for conformal coating of PCBs
•Télécharger en tant que PPT, PDF•
1 j'aime•921 vues
Conformal coating is applied to PCBs to protect against temperature, moisture and chemicals. This presentation was developed as a webinar to inform users of the options for spray, brush and dip coating. The methods are outlines and the best alternatives given for masking and de-masking for conformal coating of PCBs.
Recommandé
Contenu connexe
Tendances
Tendances (20)
Similaire à Masking for conformal coating of PCBs
Similaire à Masking for conformal coating of PCBs (20)
Plus de Bob Wettermann
Dernier
Dernier (20)
Masking for conformal coating of PCBs
- 1. Masking Alternatives for Conformal Coating of PCBs June 2018
- 2. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Masking for Conformal Coating The problem being solved What gets coated? What does not get coated. Methods Available •Tape dots •Tape shapes •Manual taping •Silicone boots •3-D printed boots •Liquid latex
- 3. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Conformal Coating Techniques (What normally gets masked) • Connectors • Test points • Switches , relays and other unsealed components • Mating sockets, pins, test and grounding points • Actuators and other electromechanical components • Batteries • Mounting holes RF filters and other devices where CC can modify values Spacers and fasteners • Potentiometers and variable capacitors • Photodiodes and sensors • Components stressed by coating eg glass MELFs • Wires for stress relief • EMI shields
- 4. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Conformal Coating Techniques Sides of metallic locations Beneath or below components Backside of leads Sides of hermetically sealed locations
- 5. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Conformal Coating Drawings What should a drawing have on it? •Coated vs uncoated areas should be obvious •What is the tolerance or overlap allowed
- 6. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net 2D vs 3D Drawings
- 7. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Conformal Coating Techniques Techniques for Conformal Coating •Brushing •Spraying •Dipping •Vacuum Chamber
- 8. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Choosing the right tape, Typical Options – Crepe masking tapes – Polyester masking tapes - Kapton ™ tapes
- 9. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Ion Chromotagraphy-Sample
- 10. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Choosing the right tape, Typical Options Evaluate on….. A.Coating dewetting? B.Filtering of CC material C.Tape residue D.Time for mask and de-mask E.Ability to be easily shaped so tape goes down to PCB and component surfaces F.Ability to prevent CC for going somewhere where you do NOT want it to go
- 11. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Dewetting NASA 8739 Specification
- 12. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Ionizer should be used! ALL masking and demasking procedures should be done in vicinity of an ionizing air blower – ESD generation
- 13. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Dots
- 14. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Position Acceptable Defect Prior to masking
- 15. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Position- Prior to masking
- 16. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Position-defect
- 17. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Shapes
- 18. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Shapes
- 19. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Tape Shapes
- 20. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Manual Shaping/Cutting of Tape
- 21. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Boots Pealable mask to seal off boot
- 22. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Boots3D Printed Boot
- 23. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Peelable Mask
- 24. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Traditional Methods Pealable Mask
- 25. Your BEST choice in PCB Test/ Rework/Repair and Solder Training & Tools www.solder.net Masking Alternatives for Conformal Coating
Notes de l'éditeur
- Review why? Want the protection of CC but only in designated areas. This protection is in the CC area and it prevents the CC from going into areas where it may harm components Where we are coning from? Looking for better ways to reduce labor NA view. Low volume. High Mix. Do not have a conformal coating dept so highly skilled people are performing masking functions Take out the labor
- CC protects PCBs against damage due to moisture, chemicals, corrosion and mechanical stresses It is applied to act as a protection against potential failure to the above over prolonged or extreme exposure AR-acrylic, UR Polyurethane, ER-Epoxy, SR-silicones Process steps Determine what you are trying to protect the PCB from Ensure assembly can be coated Determine keep out areas, spray patterns, coupon reqts etc. This is the step on the process where the kind of masking ois chosen and tooling for the masking needs to be chosen Develop the process flow-cleaning, testing, spraying, curing Clean and dry the assembly Mask the assembly Apply coating Cure coating Unmask Repair , touch up and inspect
- The previous were the process steps where masking fits in
- As important, all component edges must be entirely masked; The objective is to remove any surface breaches, eliminating coating leakage into the component. Right angle leads show their backside lead surfaces Datasheet will help determine whether sealed or unsealed Sometimes you have to see them to make that call
- Where to Coat –the drawing Requires no operator “interpretation” • Drawing should indicate where coating MUST go • Drawing should indicate where coating MUST NOT go (keep out zones) • Drawing should indicate the tolerance in the keep out Zones Drwing notes about what to do if it is outsider these boundaries 2D drawings only do so much good
- Vucuum CC not covered because not done inside of EMS firm Need to coinsider the method of coating. Dipping is more difficult and intensive process-liquid flows everywhere Type of mask chosen is a function of: types of coating-compatability, PCB’s surface geometry, the type of part to be masked and production volume
- Materials left behind by the tape SIR measurements Ionic cleanliness measurements-ion chromotograpohy (Should the test we used for SNPeel be sample? Make sure black lights are in the area for inspection Masking Tape Test To see if tape material stands up to the rigors of processing chemicals and temperatures AND will it adequately mask the areas given the adhesive system used HOW Apply tapes and spray of dip coat Problems with certain tapes-dewetting-silicone coated slitting knives in tape mfg Leaving adhesive residues-Ionic cleanliness, SIR Allow bleeding/leaking under the tape De-masking--------Tearing of tape can leave remnants and reliability concern Compatibility with a variety of CC materials
- Chlorides and some bromides will propagate electrochemical migration errors Sulfates can be corrosive and lead to dendritic growth Weak Organic Acids- WOAs – can lead to moisture absorption on the board Sodium Conductive path can be formed Ammine NH4+ Potassium, Calcium and Magnesium can also cause current leakage-
- Masking and demasking-pulling off of the tpe Bopard to be placed on static dissipative surface-make sure that the rest of the area per EOS/ESD 2020 guidelines
- Widely used masking methood Come in lots of standard sizes die cut and placed on rolls-many companies will have a variety of tapes in stock Make sure in contact with the board Make sure in contact with thesurface of the device being masked or the area being masked Adverse effects between the tape and CC can lead to demasking CC can seep underneath the tape-may cause expensive rework Adhesive residues from the tape..
- Masking not flush with the board surface Top surface of the connector is not covered
- VERY time consuming
- Lot faster than masking tape….does allow for some seepage or wicking Reduces labor-especially on complex parts May need to use liquid solder mask in addition to the modlds Nor appropriate for dipping Use a test coupon Great for high volume parts Multiple uses depending on care, material, type of coating
- Simple method- As an aside there are some hot melts being used More effective than tape dots for features with height Easier to remove than tape when wet. Put enough on there so you can remove it No fringe of dried coating at the edges does not tend to lift up the coating Application time about the same….can use it in dispense system to take out some of inconsistencies. Viscosity consistency is a challenge The pealable mask is later peeled off exposing the contact pads. In both cases above it is a good idea to remove the pealable mask or dot soon after the coating is dry to prevent tearing the coating during removal. One more good tip for clean removal of masking is to use a little thinner on a cotton bud to dampen the area at the edge of the masking. This will soften the coating eliminating tears
- Ensure that the latex materials are compatable with the PCB-some have heavy concentrations of Ammonia Dries too hard then can damage components upon removal Dries too soft then can break up easily and residues trapped underneath the devices
- JSTD-001 How to apply IPC-A-610 for inspection criteria NASA STD 8739 IPC CC-830 MIL-I-46058C