User manual

ManualsBrandsUnbranded ManualsSensorsStrain gauge

Bonding Procedures of BCM Strain Gauges

BCM SENSOR TECHNOLOGIES BVBA

Brechtsebaan 2

B-2900 Schoten - Antwerpen, BELGIUM

Industriepark Zone 4,

Tel.: +32-3-238 6469

Fax: +32-3-238 4171

website: www.bcmsensor.com

email: sales@bcmsensor.com

1. Introduction

This document describes the working steps required for bonding and soldering of BCM strain gauges on to

the load-cell element or on to the surface of the object for stress analysis. The described processes are

tailored and proven to be helpful for manufacturing of precision load cells or for precision strain

measurement. The described procedures can be applied to both foil strain gauges and semiconductor strain

gauges.

It is assumed that the strain gauges are mainly got bonded with heat curing adhesives, like BCM B-610

adhesive. So the application notes described below will mainly focus on the gauge installation with the heat

curing adhesives, especially on the use of BCM B-610 adhesive.

2. Surface Preparation

It is important to be sure that the load-cell element had no any contact with silicon-containing cutting oil

during machining. Otherwise the silicon residuals have to be removed completely by means of suitable

solvents before starting the working steps described below. This is very necessary because the smallest

amount of silicon contamination can make a bond useless. Therefore, we recommend very much to keep

the working area free from any silicon containing product.

The staff in charge of strain gauge application should know that cosmetics such as hand cream frequently

contain silicon. Therefore, it is recommended using the hand cream that is free of silicon.

2.1. Clean load-cell element first with degreasing solvent such as methyl-ethyl-ketone (MEK), acetone, or

isopropyl alcohol (IPA). After the cleaning, do not touch application area by hand for all further working

steps.

2.2. Make it ready in hand of sandpaper adhesion surface area with grit size 320 - 400 or sandblast with

aluminum oxide grit 120 - 400. When using a sandblast system, operate it with oil-free compressed air and

use it for surface preparation only. By using the system for other than surface preparation there is the

danger of contaminating the system with silicon or other chemicals that may cause a bad bond.

2.3. Remove grinding dust with a non-fluffy throw-away cloth and a solvent, e.g. IPA, or by brushing with

IPA.

2.4. If required, the position of strain gauge to be bond can now be marked by a brass needle or a hard 4H-

pencil.

3. Handling and Cleaning of Strain Gauges

Strain gauges are handled only with rounded tweezers or vacuum pen, but never touched with the fingers.

Hold the strain gauge at the backing support, not at the grid sensing area.

To manufacture high precision load cells, it is recommended to clean BCM strain gauges before the bonding

process. One can clean the gauges with ethyl alcohol, MEK, acetone, or IPA. After the cleaning, never

touch the gauges until bonding. Should the strain gauges have been touched accidentally by hand, clean it

immediately with MEK or IPA and cotton tipped applicators (do not use cotton buds with plastic grip). Put

the cleaned gauge onto a chemically cleaned glass plate with the gauge bonding side upper.

Summary of content (5 pages)

PAGE 1
Bonding Procedures of BCM Strain Gauges 1. Introduction This document describes the working steps required for bonding and soldering of BCM strain gauges on to the load-cell element or on to the surface of the object for stress analysis. The described processes are tailored and proven to be helpful for manufacturing of precision load cells or for precision strain measurement. The described procedures can be applied to both foil strain gauges and semiconductor strain gauges.
PAGE 2
Bonding Procedures of BCM Strain Gauges 4. Bonding of Strain Gauges To have quality bonding of strain gauges, utmost cleanness is essential. Therefore the bonding is preferably to be made on a dust-free workbench with filtered air supply. 4.1. Clean application area of the load-cell element with cotton tipped applicators dipped into a solvent, e.g., IPA or MEK (do not use cotton buds with plastic grip).
PAGE 3
Bonding Procedures of BCM Strain Gauges 7. Inspection of Bonding Quality The bonding quality of strain gauges can be inspected through a checking of creep errors. Generally speaking, higher positive creep are often due to the poor quality of spring element of load cells, while higher negative creep results mostly from poor installation in gauge bonding process. 7.1.
PAGE 4
Bonding Procedures of BCM Strain Gauges 9.2. The following steps may be followed when tin the gauge tabs: a) Clean solder tip and wet it with solder. b) Apply some flux to the strain gauge tab. c) Tin the gauge tab. d) After soldering, assure that the resulting solder dot is in good connection to the gauge tab. 9.3. Solder the wire to the gauge as follows: a) Cut wire to length, remove insulation and tin the ends, using the same solder as in the step 9.2.
PAGE 5
Bonding Procedures of BCM Strain Gauges 14.2. For the load-cell element made from aluminum alloy, it is recommended to apply the following conditions: curing pressure: 1 ~ 3 bar curing temperature: 135 °C for 2 hours post cure temperature: 165 °C for 2 hours However, for some types of aluminum alloys these temperatures may be too high. In such a case the staff in charge of strain gauge application had better apply the maximum permissible temperature and extend the curing time to 4 hours.