Case Study (Page 2)
Our Further Analysis:
We were given a spare unassembled board and asked to investigate further:
- The board exhibited a bow of almost 5% when measured. We then measured a number of copper features at the extremes of the panel and found them to be up to 0.3mm less than the dimensions in the Gerber data.
- There was evidence of the solder resist dams breaking down on some of the finer pitch dimensions and encroachment of the component notation onto solder-able areas.
- The surface conductors width and spacing were measured and were within tolerance indicating that without further testing the impedance values should be within tolerance.
We asked the customer if the boards had been supplied with impedance results, impedance coupons or any micro-section analysis. The boards had only been supplied with a certificate of conformity.
The customer was becoming increasingly nervous about our findings. The customer contacted the manufacturer again who agreed that the bow and twist was caused by poor copper distribution, they stated that they carried out routine micro-sections but these were not available to the customer.
We were asked to carry out micro-sections on the board to investigate further.
Our Micro-section Analysis:
- Micro-sections were taken from two diagonally opposed corners and a further one from the centre of the board. Analysis confirmed various issues with the board, the copper weights for all layers were 1oz including the signal layers which had been specified as 0.5oz. The dielectric spacing was not as per specification with up to 2 thou variations observed.
- The micro-section from the centre of the board was thermally shocked for 10 seconds at 288°C and evaluated. It showed poor drill quality with a large degree of nail heading at the inner layer interface as well as some micro de-lamination. The copper plating thickness in the hole ranged from 25microns at the outer surfaces down to 12 microns in the centre of the holes. The inner layer registration to the hole pattern was very poor, with breakout on some layers.
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