W-Linx Technology TXE-418-KH PAD Layout, Production Guidelines, Hand Assembly Automated Assembly

PAD LAYOUT

The following pad layout diagram is designed to facilitate both hand and automated assembly.

0.065"

0.610"

0.070"

0.100"

Figure 14: Recommended PCB Layout

PRODUCTION GUIDELINES

The modules are housed in a hybrid SMD package that supports hand or automated assembly techniques. Since the modules contain discrete components internally, the assembly procedures are critical to ensuring the reliable function of the modules. The following procedures should be reviewed with and practiced by all assembly personnel.

HAND ASSEMBLY

AUTOMATED ASSEMBLY

For high-volume assembly, most users will want to auto-place the modules. The modules have been designed to maintain compatibility with reflow processing techniques; however, due to the their hybrid nature, certain aspects of the assembly process are far more critical than for other component types.

Following are brief discussions of the three primary areas where caution must be observed.

Reflow Temperature Profile

The single most critical stage in the automated assembly process is the reflow stage. The reflow profile below should not be exceeded, since excessive temperatures or transport times during reflow will irreparably damage the modules. Assembly personnel will need to pay careful attention to the oven’s profile to ensure that it meets the requirements necessary to successfully reflow all components while still remaining within the limits mandated by the modules. The figure below shows the recommended reflow oven profile for the modules.

	300	Ideal Curve	Forced Air Reflow Profile
		Limit Curve
	250		220oC
	200		210oC
C)			o
o			180 C
(

Pads located on the bottom of the module are the primary mounting surface. Since these pads are inaccessible during mounting, castellations that run up the side of the module have been provided to facilitate solder wicking to the module’s underside. This allows for very quick hand soldering for prototyping and small volume production.

Soldering Iron
Tip
Solder
PCB Pads	Castellations

Figure 15: Soldering Technique

Temperature	150		125oC								Reflow Zone
	100								Soak Zone		20-40 Sec.
								2 Minutes Max.
	50					Preheat Zone
		Ramp-up				2-2.3 Minutes									Cooling
	0	1-1.5 Minutes
	0	30		60	90		120		150	180		210	240	270		300	330	360

Time (Seconds)

Figure 16: Maximum Reflow Profile

If the recommended pad guidelines have been followed, the pads will protrude slightly past the edge of the module. Use a fine soldering tip to heat the board pad and the castellation, then introduce solder to the pad at the module’s edge. The solder will wick underneath the module, providing reliable attachment. Tack one module corner first and then work around the device, taking care not to exceed the times listed below.

Absolute Maximum Solder Times

Hand-Solder Temp. TX +225°C for 10 Seconds Hand-Solder Temp. RX +225°C for 10 Seconds Recommended Solder Melting Point +180°C Reflow Oven: +220°C Max. (See adjoining diagram)

Shock During Reflow Transport

Since some internal module components may reflow along with the components placed on the board being assembled, it is imperative that the modules not be subjected to shock or vibration during the time solder is liquid. Should a shock be applied, some internal components could be lifted from their pads, causing the module to not function properly.

Washability

The modules are wash resistant, but are not hermetically sealed. Linx recommends wash-free manufacturing; however, the modules can be subjected to a wash cycle provided that a drying time is allowed prior to applying electrical power to the modules. The drying time should be sufficient to allow any moisture that may have migrated into the module to evaporate, thus eliminating the potential for shorting damage during power-up or testing. If the wash contains contaminants, the performance may be adversely affected, even after drying.

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