DFPS Base and Service Board (A3043)

© 2022 Kevan Hashemi, Open Source Instruments Inc.

Contents

Description
Versions
Design
Development

Description

[00-SEP-22] The Direct Fiber Positioning System (DFPS) Base and Service Board (A3043) consists of a base board that holds sixteen fiber positioners and a service board that provides sixteen twelve-way connectors for fiber controllers. The two boards are joined by a flex cable that carries sixty-four electrode voltages for the sixteen positioners. Sixteen DFPS Fiber Controllers (A3045A) plug into one side of the service board. On the other side \is a ten-way connector that plugs into a DFPS Backplane (A3044A).


Figure: Drawing of Base and Service Board, Bottom Side.

The base board and service board are roughly 19 mm square. They must fit inside a 20-mm square envelope so that we can maintain a 5-mm × 5-mm density of fibers.


Figure: Three 4×4 Positioner Cells On Bridge with Frame. The frame bolts to our motorized, two-axis gimbal.

We build the Base and Service Board (A3043) on a rigid-flex printed circuit baord (PCB). The base board portion has a separate top-layer circuit board holding electrode pins that we glue onto the base-board section of a six-layer rigid-flex board. The flex cable arises from the two center layers of the six-layer PCB. The service board portion consists of a rigid square with sixteen connectors soldered on the PCB top-side and one connector soldered on the PCB bottom-side. When we load the A3043 into our positioning system, we bend the flex so that the PCB top-side of the service board becomes the under-side with respect to vertical. The fiber controllers plug into the underside while the connetor on the upper-side plugs into the under-side of the backplane.

Versions

The following versions of the DFPS Base and Service Board (A3043) exist.

Version Actuator Geometry Controller Comment
A Any with 3.8-mm OD actuator 4 × 4 on 5-mm grid A3045A For sixteen-fiber cells.
Table: Versions of the DFPS Base and Service Board (A3043).

Design

A3034A_Drawing.gif: Base and Service Board Drawing.
A304301A.zip: Service Board PCB Version A.
A304302Y.zip: Base Board PCB Version Y.
A304302Y_Top.svg: Top view of A304302Y.
A304302Y_Bottom.svg: Bottom view of A304302Y.
A304302Y.dxf: Drawing of A304302Y.
A304301X.zip: Bottom layer of base board Version X.
A304301X_Top.svg: Top view of A304301X.
A304301Y.zip: Bottom layer of base board version Y.
A304301Y_Top.svg: Top view of A304301Y.
A304301Y_Bottom.svg: Bottom view of A304301Y.
A304301Y.dxf: Drawing of A304301Y.
A304302X.zip: Top layer of base board version X.
A304302X_Top.svg: Top view of A304302XR2.
A304302X_Bottom.svg: Bottom View of A304302X.

Development

[08-JUN-22] Draft layouts of top and bottom layer 61-mil thick circuit boards that we will glue together to form the 125-mil thick base board with counter-sinks for the positioner end caps.

[23-JUN-22] Our A304301X board looks good, see photo below. Our A304302XR1 has a problem: our Gerber files included a copper annulus around the actuator holes, which will short the electrodes. We prepare A304302XR2 with no copper around the actuator holes top or bottom, and no solder mask clearance on the top side.


Figure: A304301X, Top Side. Shown with 1.25-mm diameter ferrule.

[15-AUG-22] We are trying to devise a way to assemble the two layers of the base board, allowing for the top layer to be rigid only, the bottom layer to be rigid-flex, in which the top and bottom layers are well-aligned with pins, the actuators are provided with protruding pins for their electrode contacts, the electrode connections are made through the caps of these actuator pins being surface-mount (SMT) soldered in our SMT reflow oven, and we glue the sixteen positioners into the base board at the same time we glue the base board to the base plate in our assembly jig.


Figure: Base Board Layers Fastened with Pins. Four pins hold the base board layers together. Sixteen pins provide electrode voltages for actuators.

After soldering all the actuator pins to the top side of the top layer, we apply solder paste to the caps of these pins, fasten the bottom layer to the top layer with four pins that we hand-solder to the top side of the top layer and the bottom side of the bottom layer, then place in the reflow oven to get the actuator pin heads to weld to the pads on the top side of the bottom layer. One concern is the distance between the flange of the ferrule that will mount in the top layer hole.


Figure: Ferrule Gap Close-Up. Actuator pin cap to metal of flange appears to be ≥0.5 mm.

Another concern is our ability to solder the actuator pins to the electrodes of the actuators in the center of the 4 × 4 array. One plan is to hand-solder with a soldering tip that is less than 1.4 mm wide. Another is to apply solder paste to all the pins with a syringe tip 1-mm in diameter, then place in the reflow oven. In both cases, we remove the entire positioner cell from our assembly jig, so that we have the base plate, base baord, and its sixteen positioners glued together. We place on our work surface and rotate to give ourselves access from all sides.

[16-AUG-22] We submit A304301Y and A304302Y for fabrication, width 0.8 and 1.6 mm respectively, with CNC machining for the borders.

[25-AUG-22] We receive A304301Y and A304302Y. We assemble with the sixteen electrode pins and four fiducial pins. Alignment of the ferrule and flange holes appears perfect. We are able to solder positioners to the pins easily. We did not add paste to the electrode pin heads. Next time, we will add the paste before joining the two boards, place in oven, and see if we can get all sixty-four pins to weld to the pads on the lower layer.

[09-SEP-22] Base and Service Board rigid-flex PCB A304301A layout is done. We are checking the netlist. The board is six layers with 4-mil tracks, 5-mil spacing, and a two-layer central flex portion that joins the base and service sections.