Manufacturing method for a secure-digital (SD) flash card with slanted asymmetric circuit board
A flash-memory device has a printed-circuit board assembly (PCBA) with a PCB with a flash-memory chip and a controller chip. The controller chip includes an input/output interface circuit to an external computer over a Secure-Digital (SD) interface, and a processing unit to read blocks of data from the flash-memory chip. The PCBA is encased inside an upper case and a lower case, with SD contact pads on the PCB that fit through contact openings in the upper case. Supporting end ribs under each of the SD contact pads and middle ribs support the PCB at a slanted angle to the centerline of the device. The PCB slants upward at the far end to allow more thickness for the chips mounted to the bottom surface of the PCB, and slants downward at the insertion end to position the SD contact pads near the centerline.
1. A method for manufacturing a flash-memory device comprising:
forming contact pads on an upper surface of a printed-circuit board (PCB);
forming a PCB assembly by soldering a flash-memory chip onto a lower surface of the PCB and soldering a controller chip to the lower surface of the PCB;
wherein the contact pads are for carrying signals from an external computer to the controller chip to instruct the controller chip to read blocks of data from the flash-memory chips;
forming an upper case by molding plastic;
forming locking tabs on the upper case when forming the upper case;
forming a lower case by molding plastic, the lower case having an outside surface as a largest external surface of the lower case;
forming engagement slots on the lower case when forming the lower case;
forming supporting ribs on the lower case when forming the lower case, the supporting ribs for supporting the PCB assembly at a slanted angle within the lower case wherein the upper and lower surfaces of the PCB are not parallel with the outside surface of the lower case;
fitting the PCB assembly into the upper case to form a sub-assembly of the PCB assembly and the upper case;
sliding the upper case into the lower case until the locking tabs on the upper case snap into the engagement slots on the lower case to secure the upper case to the lower case;
wherein the upper and lower surfaces of the PCB are not parallel with the outside surface of the lower case;
whereby the PCB assembly is at the slanted angle within the lower case when the flash-memory device is assembled using a snap-together process.
2. The method of claim 1 further comprising:
inserting an upper adhesive film between the PCB assembly and the upper case during assembly;
inserting a lower adhesive film between the PCB assembly and the lower case during assembly;
whereby the upper adhesive film bonds the upper case to the PCB assembly and the lower adhesive film bonds the lower case to the PCB assembly during assembly.
3. The method of claim 1 further comprising:
forming end ribs inside the lower case when forming the lower case, wherein each end rib is located directly underneath a contact pad on the upper surface of the PCB when assembled;
wherein the end ribs increase rigidity of the contact pads within the lower case.
4. The method of claim 1 wherein the contact pads are below a center-line between the upper case and the lower case when assembled;
wherein the PCB is slanted upward and is above the center-line at the flash-memory chip, whereby the PCB straddles the center-line for an asymmetric flash-memory device design.