How good are current PCB debugging tools? [closed]

Question

I'm a newbie in the field of manufacturing, and I'm hoping to get a broad understanding of the field. After you get PCBs manufactured, I understand that you need to check for mechanical damage, scratched copper, through-hole misalignment, cold solders, solder bridging, etc.

If I understand correctly, you can check for these either (1) visually, (2) with "bed of nails" test bed, or (3) with JTAG.

In what contexts are each of these 3 methods used? Are there other methods besides these? Is one preferred over the others? How effective, cheap, and easy are each of these solutions? What are the hardest parts of the process of debugging?

Answer 1

How good are current PCB debugging tools?

Modern tools are very good at testing CCAs.

Here are some of the common tools that are used in the electronics industry.

Automated Optical Inspection (AOI)
AOI equipment uses a camera to look for missing parts, mis-placed parts, and bad solder joints.

This is typically the first test after a board is assembled.

X-RAY Inspection
If the board contains no-lead parts or Ball Grid Array (BGA) parts, then AOI can't inspect all the solder joints. In this case X-Ray inspection equipment is used to verify that the solder joints under these parts don't have defects.

Automated Test equipment (ATE)
After being assembled the CCAs can be plugged into automated test equipment. The ATE applies input signals and commands to the card and then measures the response. ATE can perform tests much faster and more accurately than factory technicians can test by hand.

Good ATE should make measurements for each function that the card is required to perform.

ATE usually involves some custom-built hardware and wiring harnesses to test each design.

Flying Probe
Companies like SPEA make flying probe equipment.

For bare PWBs, the board house can conduct tests for electrical continuity and isolation using a flying probe.

For assembled boards, a flying probe can make measurements of individual components. This can be used to verify that the parts are the correct part (right value of resistor/capacitor), or that they were placed correctly (diode not backwards).

JTAG
For boards that have chips with JTAG boundary scan, this method can be used to measure each IO pin on the chips in the scan chain. It can also be used to inject stimulus from those IO pins to other chips (which may or may not be on the chain).

Answer 2

It's hard to discuss testing as a stand alone entity. Depending on your product and industry, there may be multiple assembly/inspection/test steps in the manufacturing flow. Here's what's typically done for hi rel production systems.

First of all, we usually don't do x-ray inspection on a routine basis. That's reserved for troubleshooting. JTAG is usually only used to program FPGAs and like devices on the board. That leaves ATE or manual testing. Here's a typical product flow. Note that I have left out some steps.

1. Install components on the PWB. This is usually a solder reflow operation, though there may be some manual operation for specific parts.
2. AOI (optical) inspection
3. Rework as required
4. Manual inspection
5. Attach (solder) connector to the board
6. Inspection
7. Half dozen or so temperature cycles
8. Test at ambient, cold, and hot
9. Clean and conformal coat
10. More manual visual inspections
11. One final test at ambient
12. Final inspection

This flow is oriented to finding problems as early in the production process as possible. You don't want a marginal part or bad solder joint to only be uncovered during final test of the system, or after it's been delivered to the customer.