When Did They Change the Build Quality of the Spice Series?

[Moggul]

From this very site:

https://www.hpmuseum.org/tech30.htm

For the 30 series, HP designed an entirely new way of assembling their calculators. Behind the keyboard was a thick sheet of metal. On the back of this sheet was a foam pad and a single flexible circuit was wrapped around the metal/foam board. In front, an insulating sheet with holes for key contacts was placed over the flexible circuit and a snap disk contact sheet was placed over that and spot welded into place. (The welds made contact between the snap disk contact traces and the main flexible circuit.)

The flexible circuit wrapped around the metal and was attached to the foam in back. A hard plastic backbone held the chips in place on the flexible circuit with the foam supplying pressure against the circuit under the chip leads. The chips were NOT soldered to the circuit!

This arrangement was quite easy to assemble and also gave the 30 series keyboard a level of rigidity even greater than that of the 20 series while still making keyboard repairs easy as on the Classic series. (The 20 series heatstaking made keyboard repairs difficult.)

Unfortunately, the original design didn't measure up to the reliability of earlier HP calculators so HP redesigned the 30 series interior. The redesigned models used a more conventional design with a single rigid circuit board with snap disks on one side and ICs soldered in place on the other side. A plastic spine provided extra rigidity but didn't hold the chips in place as on the earlier version. These later models weigh about 1.5 oz less due to the removal of the metal sheet.