Leadless ceramic chip carriers

The requirements for advanced military MLBs are shown in Table I. One of the major problems of using leadless ceramic chip carriers in advanced avionics (VHSIC and VLSI) applications is the mismatch between the CTE of alumina chip carriers (6.4 ppm/°C) or silicon (3 ppm/°C) and conventional glass/epoxy substrates (12 to 17 ppm/°C). This mismatch results in work-hardening and cracking of solder joints which attach the devices to the substrate. 

MISMATCH OF THERMAL EXPANSION. The thermal expansion mismatch of organic substrates and leadless ceramic chip carriers has been widely reported, and a great deal of development work was carried out. However, the actual number of these packages used worldwide is small, and many of those overcome the problem by using clips and sockets. 

Surface mounting of plastic packages is quite feasible with current standard materials, and improvements in mechanical properties will enhance this. Where leadless ceramic chip carriers have to be used there are now satisfactory products available. 

Leadless ceramic chip carrier (LCCC), or ceramic leadless chip carrier. JEDEC registered type A must be socketed when on a printed circuit board or a ceramic substrate board, and type B must be soldered. The LCC minipack must be soldered onto printed circuit boards. 

Little foot (a trademark of Siliconix), a tiny small outHne integrated circuit (SOIC) package. Leadless ceramic chip carrier (LLCC). 

The discussion of lead properties of course does not apply to leadless devices such as leadless ceramic chip carriers (LCCCs). Design teams using these and similar packages must understand the better heat transfer properties of the alumina used in ceramic packages and must match coefficients of thermal expansion (CTEs or TCEs) between the LCCC and the substrate since there are no leads to bend and absorb mismatches of expansion. Use of ceramic devices may lead the design team to consider the use of Low Temperature Co-fired Ceramic (LTCC) substrates and assembly technologies XXX. 

Aramid. A better solution for CTE match is to use a non-woven aramid mat material that is resin-impregnated it is available with either modified epoxy or polyimide resins. Non-woven aramid has lower in-plane expansion under heat input, and is closer to the in-plane expansion of leadless ceramic chip carriers (LCCCs) or thin small outline packages (TSOPs). A low in-plane expansion reduces the strain on the solder joint, which in turn improves assembly yields and long-term field reliability. 

Leaded vi. Leadless Surface-Mount Components. Leadless surface-mount components with peripheral solder joints (e.g., leadless ceramic chip carriers, LCCCs) are more susceptible to solder joint failures due to thermal and mechanical stresses than leaded components because there is no compliance in the system (see Fig. 57.21). A compliant lead can take up relative displacement between the component body and the substrate during mechanical or thermal stressing. In doing so, it minimizes the stress and strain imposed on the solder joint, thus reducing the likelihood of failures. Large leadless components should be avoided whenever possible. If they must be used, the substrate must have as close a CTE mismatch as possible and be protected from mechanical stresses. A conformal coating should be considered. 

ACF anisotropic conductive film LCCC leadless ceramic chip carriers... 

Often, detector arrays are adhesively mounted in leadless ceramic chip carriers (LCCs). Electrical leads are plated on the surface of the LCC and mate with matching spring-loaded, gold-plated contacts in a socket that can be mounted in a dewar, while allowing the flat back of the LCC to be pressed against the dewar s cold surface. In this case, a 3-5 mil (0.003-0.005 in.) thick sheet of indium is placed between the... 

FPAs are commonly mounted on a leadless ceramic chip carrier (LCCC - but sometimes seen as LCC) for wire-bonding before test, and for the test itself. The common LCCCs sizes have 68, 84, 100, and 124 pins. These typically have bottom contacts for interfacing to a standard test socket. 

Accelerated Thermal Cycle Testing. The mechanical property data was included as part of the quantitative down-selection process based on a thermomechanical fatigue (TMF) test the test vehicle consisted of a 441/0 leadless ceramic chip carrier (LCCCs-44) with only corner leads soldered to provide conditions for high stress. Test parts were thermally cycled between —55 and + 125 ° C at the rate of 24 cycles per day. The TMF data was expressed as the number of cycles-to-failure for an alloy expressed as a percentage of the cycles-to-failure for eutectic Sn-Pb solder. 

A thermomechanical fatigue screening test for the remaining 13 alloys was performed utilizing 44 I/O and 20 I/O leadless ceramic chip carriers (LCCC) on FR-4 PWB substrates under the thermal cycling test conditions of —55 to + 160°C, with a ramp rate of 10°C/min, temperature dwell of 10 min at each temperature extreme for a total cycle duration of 1 hr. The WeibuU results for the various alloys are presented in Figure 29. The seven alloys determined to be the best performers based on mean life are listed in Table 41 The alloy Sn-A.8Bi-3.3Ag... 

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