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Differences connector design details can directly lead to the selection of housing materials. So how to choose DDR4 memory module connector material? Select the connector housing material must have extreme mechanical and thermal properties to withstand peak temperatures of about 10 seconds. Also, the material must be properly balanced by low hygroscopicity and high surface tension, to avoid high temperature infrared reflow (IR-reflow) is formed during the process of so-called bubble. In the electronics industry, green design (GreenDesign) is the focus of the industry. In addition to reducing energy consumption, the industry is increasingly restrict the use of certain halogen as flame retardant in the connector housing. Support the next generation of green design (GreenDesign) memory device must meet to improve performance, increase power density, improve reliability, lower power consumption and avoid the use of hazardous substances, and many other requirements, which is the latest generation of this market background DDR4 SDRAM device's computer memory situation.
This paper discusses the various halogen-free (halogen-free) for DDR4 socket development work, and according to strict specifications and IEC61249-2 JEDECDDR4 halogen-compliance, to discuss different options for housing material. We examined a variety of high-performance polymers, such as liquid crystal polymer (liquidcrystalpolymer, LCP), polyamide PA4T and different polyphthal amide (polyphthalamide, PPA), and focus on the key parameters related features, such as connection reliability, pin holding force, warping, and the linear thermal expansion matching system PCB (CLTE). Termination Method DDR4 connector means connecting one terminal terminating a conductor, and a method for terminating ensure good electrical contact stability, gas-tight connection is prevented from corrosion. DDR4 connector termination methods are commonly used:
● Surface Mount Technology (SMT) (This is a design trend)
● Pin Through Hole (PTH) (current mainstream technology)
● Through Hole Reflow (PininPaste) (mainly for-one PC)
● press-fit (mainly for telecommunications) connector warpage
When the connector is soldered to the PCB coplanarity loss occurs connector warp (warpage) case. Such warping is a complex phenomenon, affected by various parameters, such as the connector housing material for heat distortion temperature (heatdistortiontemperature, HDT) comparing the thermal expansion coefficient (comparetivethermalexpansion, CTE) between the plastic housing and PCB type, shell materials and mobility, and the associated stresses generated during injection molding the housing. Systems of linear thermal expansion (CLTE) in order to achieve good coplanarity connectors on FR4 or the latest halogen (halogen-free) PCB, must try to make CLTE matching circuit boards and connectors between the shell material. In addition, the need to combine high hardness and high deflection temperature under load (highdeflectiontemperature, HDT), to ensure that low warpage after reflow.
In order to produce high-quality mobility DDR4 connector, while keeping costs affordable OEM manufacturers, manufacturers looking for housing material needs to have the greatest possible mobility and meet other critical design requirements such as coplanarity. High flow material of a high number of filled cavity (cavity) in the injection molding process. Furthermore, a single injection molding machine can produce more housing, thereby reducing manufacturing costs. Meanwhile, the high flow material means less stress tolerance of the housing, exposed to high temperatures because less stress during assembly of the connector. As a result, the connector may be warped, and in particular, the ends of the signal pins may lose electrical connection with the PCB, resulting in much higher manufacturing cost than the cost of maintenance.
Traditionally, when the injection manufacturer or connector manufacturer for high mobility materials, liquid crystal polymer (LCP) is usually the preferred material. Pin Pin retention force holding the terminal in the housing cavity. Prevent prolapse terminal or terminals loose. Typically, the locking device is called tangs (tang) of a spring-like pressure to the terminal in the housing wall. "Contact holding force on the housing" specification describes the terminal pull force required for proper installation. Conclusion polyamide PA46 and PA4T reference materials currently used for DDR1 to DDR3 designed to successfully develop DDR4 design only requires in-depth understanding of applications and materials, and connector manufacturers, material suppliers and major OEM manufacturers must work closely .
DDR4 design challenges as well as various changes compared to the previous DDR3 technology, greatly improving the mechanical strength, pin retention and mobility applications. Since PA46 has excellent flowability and mechanical properties in combination, and it is most suitable for a press-fit design PTH material. PA4T of about 25 ℃ higher melting point, higher hygroscopicity and lower the surface tension is considered to be the preferred material for SMT and ULP design. Warping has a key challenge in the server using DDR3 connector, with the SMT, and using ULP VLP design increases, the number of each server socket board DDR increasing warping has become an increasing challenge. PA46 and PA4T material with outstanding coplanarity, significantly reducing costly rework and rework PCB-risk, high mechanical strength and low warpage LCP makes DDR4 technology can not meet the application requirements. Electronics industry increasingly concerned about sustainable development, not only focus on avoiding the use of hazardous substances, in line with the EU's RoHS Directive 2011/65/EU, but also fully compliant Halogen IEC61240-2-21's. Polyamide PA46 and PA4T ensure full compliance with the requirements of halogen-free flame retardants, thus avoiding the connector manufacturer, or OEM manufacturer for further re-verify eligibility requirements.