Micro-Machine-Ability For Back End Test Sockets (Back End Test Part Two)

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In the Back End Test socket market we have concluded that the machined features continue to miniaturize driven by Moore's Law and the decreasing chip size.

The fact is, not all plastic materials are capable of machining the minute features to the desired quality levels. Plastic materials move, its what makes them plastic. So how does one evaluate the various materials for increasing micro-machinability?

First let's define the critical properties in the micro machining of plastic materials for Test Sockets. 

THERMAL - Glass Transition Temperature (Tg) is the point where amorphous materials soften. Melting Point (MP) is the point a crystalline material moves from a solid phase to a liquid phase.

These properties are critical to micro machining in that high frictional heat is generated by the micro drilling, and the result can lead to what is commonly referred to as burrs. Materials with higher thermal property tends to resist burring and thus machines better holes. 

MECHANICAL - Tensile Elongation has been found to have a direct impact on hole accuracy. (See #SemiconScott - Hole Accuracy in Micro Machining).

The softer the compressibility, the more likely the drill bit is to dance on the surface before it penetrates. 

FILLER - Fillers are often added to increase the dimensional stability of a material such as glass fiber or ceramic. But these fillers can have an adverse effect on the quality of the minute holes.

Drilling into glass is not optimal for producing a clean minute hole, That said we apply a 75% penalty for fiber filled content and a 25% penalty for particulate fill such as ceramic. 

Formula for comparing micro machinability: 

Tg or MP - Tensile Elongation/100 = Machinability Factor

Machinability Factor X Filler Penalty = Revised Machinability Factor for Filled Materials 

The higher the machinability Factor, the more machinable for fine features in the material. 

Polymer TG MP Tensile Elogation Filler Factor Machine-ability Factor
Texasint LP PI 752 5 0 7.5
Standard Polyimide 752 7.5 0 7.4
Semitron MDS-100 350 1.5 0 3.5
Ultem 1000 (PEI) 410 80 0 3.3
Semitron MP-370 320 3 (0.90) 2.9
TECAPEEK CMF 290 3 (0.90) 2.6
Kyron GC 100 290 1 (0.90) 2.6
GP PEEK 290 40 0 2.5
Kyron 2204 289 21 (0.90) 2.4
PEI (UItem) + Glass 527 4 (0.25) 1.3




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Micro-Machine-Ability BET Part Two - PDF