Outline
This procedure describes the use of flat set eyelets for the repair of a through connection that has an inner layer connect. No surface wire is used. The inner layer reconnect is established by soldering the barrel of an eyelet to the exposed inner layer, and the connection is encapsulated in high-strength epoxy.Caution: This is a complex repair procedure that demands the proper tools and materials. To expect reliable results, repair technicians must have a high level of expertise. Use this method only when alternative methods are unacceptable. Caution: This procedure requires very accurate control over the location and depth of a milled hole. It is recommended that a precision drill system be used in combination with a high-power stereo microscope.
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Images and Figures![]()
Damaged Plated Hole with Inner Layer Connection.
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Figure 1: Precision Drill System shown with circuit board pinned in place.
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Figure 2: Mill down to and expose inner layer signal or plane.
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Figure 3: Solder the eyelet barrel to the exposed inner layer signal or plane.
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Figure 4: Fill the milled hole with the epoxy up to, and level with, the surface of the board.
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Figure 5: Set the eyelet using an Eyelet Press or using a Tool Grip and Setting Tools.
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Figure 6: The small cone tip end of the lower Setting Tool faces up. The large cone end of the upper setting tool faces down.
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Figure 7: Flare the eyelet barrel using the flare end of the setting tool.
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Figure 8: Flatten the eyelet barrel using the flat end of the setting tool.
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Figure 9: Eyelet barrel formed flat to circuit board surface.
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Figure 10: Flat flange eyelet.
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Figure 11: Funnel flange eyelet.
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Procedure
Eyelet Selection Criteria
ID - Inside Diameter The eyelet inside diameter should be a .075 - .500 mm (.003"-.020") greater than the component lead diameter. OD - Outside Diameter The clearance hole drilled through the circuit board should allow the eyelet to be inserted without force but should not exceed .125 mm (.005") greater than the eyelet's outside diameter. LUF - Length Under Flange The length of the eyelet barrel under the flange should be .630 - .890 mm (.025" - 035"), greater than the thickness of the circuit board. This added length allows for proper protrusion when setting the eyelet. FD - Flange Diameter The eyelet flange diameter should be small enough to prevent interference with adjacent lands or circuits. Note: Be sure to select an eyelet meeting the proper criteria. An eyelet with an oversize flange may interfere with adjacent circuits. An eyelet that is too short will not protrude through the circuit board for proper setting. Procedure
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